Firstly: 

Jihad in Arabic means striving and doing one’s utmost in word and deed. 

In Islamic terminology it refers to the Muslims striving to fight the kuffaar so that the word of Allaah will be supreme. 

See: al-Nihaayah fi Ghareeb al-Hadeeth by Ibn al-Atheer (1/319); al-Misbaah al-Muneer (1/112); Ahammiyyat al-Jihaad by Dr. ‘Ali ibn Nufay’ al-‘Alyaani. 

Secondly: 

Shahaadah in Arabic has several meanings: definitive news, being present, seeing something, openness, and dying for the sake of Allaah. 

In Islamic terminology it refers to those Muslims who die fighting the kuffaar and because of the fighting. With regard to the Hereafter, it may refer to other things as well,  as we shall see below. 

See: al-Mawsoo’ah al-Fiqhiyyah (26/214, 272). 

Thirdly: 

Martyrs are of different types. 

Al-Nawawi (may Allaah have mercy on him) said: 

It should be noted that martyrs are of three types: 

1 – The one who is killed in a war against the kuffaar by any means of fighting. He comes under the heading of martyrs who are rewarded in the Hereafter and he comes under the rulings on martyrs in this world, i.e. he should not be washed and the funeral prayer should not be offered for him. 

2 – The one who is given the reward of the martyr but does not come under the rulings on martyrs in this world. This refers to those who die of stomach diseases, the plague, being crushed under a falling wall, those who are killed defending their wealth and others who are mentioned in the saheeh ahaadeeth as being described as martyrs. Such a person should be washed and the funeral prayer should be offered for him, but in the Hereafter he will have the reward of the martyrs, but it will not necessarily be the same as the reward for those in the first category. 

3 – Those who steal from the war booty etc, who it says in the reports cannot be regarded as martyrs if they are killed in a war against the kuffaar. Such a person comes under the ruling of martyrs in this world, so he should not be washed and the funeral prayer should not be offered for him, but he will not have the full reward in the Hereafter. End quote. 

Sharh al-Nawawi ‘ala Muslim (2/164). 

Degrees of martyrs: 

The status of the martyr is high indeed, coming after the Prophets and Siddeeqs in status. 

Shaykh al-Islam Ibn Taymiyah(may Allaah have mercy on him) said: 

Allaah says (interpretation of the meaning): 

“then they will be in the company of those on whom Allaah has bestowed His Grace, of the Prophets, the Siddeeqoon (those followers of the Prophets who were first and foremost to believe in them, like Abu Bakr As‑Siddeeq رضى الله عنه ), the martyrs, and the righteous”

[al-Nisa’ 4:69]

These are the four degrees of Allaah’s slaves: the best of them are the Prophets, then the Siddeeqs, then the martyrs, then the righteous. End quote. 

Majmoo’ al-Fataawa (2/223). 

Allaah has made Paradise of varying levels or degrees, of which the Mujaahideen (those who strive in jihad) will have one hundred degrees, as it was narrated in al-Saheeh from the Prophet (peace and blessings of Allaah be upon him), therefore the martyrs are not all of the same status, rather they vary in status. 

Ibn Hajar (may Allaah have mercy on him) said, after listing the martyrs other than those who are killed in battle: 

We have compiled from excellent sources more than twenty types… 

Ibn al-Teen said: All of these ways of dying are painful. Allaah has favoured the ummah of Muhammad (peace and blessings of Allaah be upon him) by making it a means of purifying them from sin, increasing their reward and causing them to attain thereby the status of the martyrs. 

I (Ibn Hajar) say: It seems that those mentioned are not all of the same status. This is indicated by the report narrated by Ahmad and Ibn Hibbaan in his Saheeh from Jaabir, and by al-Daarimi, Ahmad and al-Tahhaawi from ‘Abd-Allaah ibn Hubshi, and by Ibn Maajah from ‘Amr ibn ‘Anbasah: that the Prophet (peace and blessings of Allaah be upon him) was asked: What type of jihad is best? He said: “The one whose horse is killed and whose blood is shed.” End quote. 

Fath al-Baari (6/43, 44). 

In the saheeh Sunnah there are reports from the Prophet (peace and blessings of Allaah be upon him) which indicate this difference in status among the martyrs. 

For example: 

(a)

It was narrated from Nu’aym ibn Hammaar that a man asked the Prophet (peace and blessings of Allaah be upon him): Which of the martyrs is best? He said: “Those who, when they took up their position in the ranks, did not turn their faces away until they were killed. They will be in the dwellings on high in Paradise, and their Lord smiles upon them, and when your Lord smiles upon a slave in this world, he will not be brought to account.” 

Narrated by Ahmad (21970); classed as saheeh by Shaykh al-Albaani in al-Silsilah al-Saheehah (2558). 

(b)

It was narrated that ‘Utbah ibn ‘Abdin al-Sulami said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “The slain are of three types: (the first is) a believing man who fought with his life and his wealth for the sake of Allaah, and when he met the enemy he fought them until he was killed. That is the proud martyr who resides in the tent of Allaah beneath His Throne; the Prophets are no better than him except by virtue of their being Prophets. (The second is) a believing man who committed some sins, but he fought with his life and his wealth for the sake of Allaah, and when he met the enemy he fought until he was killed. His sins are erased, for the sword erases sins, and he will be admitted through whichever of the gates of Paradise he wishes, for it has eight gates, and Hell has seven gates, and some of them are better than others. (The third is) a hypocrite who strove with his life and his wealth, and when he met the enemy he fought for the sake of Allaah and was killed. He will be in Hell, for the sword does not erase hypocrisy.” 

Narrated by Ahmad (17204). Its isnaad was classed as jayyid by al-Mundhiri in al-Targheeb wa’l-Tarheeb (2/208), and as hasan by al-Albaan in Saheeh al-Targheeb (1370). 

(c)

It was narrated from ‘Abd-Allaah ibn Hubshi al-Khath’ami that the Prophet (peace and blessings of Allaah be upon him) was asked: What type of jihad is best? He said: “The one who strives against the mushrikeen with his wealth and his life.” It was said: What kind of death is noblest? He said: “The one whose blood is shed and his horse is killed.” Narrated by Abu Dawood (1449) and al-Nasaa'i (2526); classed as saheeh by al-Albaani in Saheeh al-Targheeb (1318). 

(d)

It was narrated from Jaabir (may Allaah be pleased with him) that the Prophet (peace and blessings of Allaah be upon him) said: “The leader of the martyrs is Hamzah ibn ‘Abd al-Muttalib and a man who stood up before a tyrant and enjoined good and forbade evil, and he killed him.” Narrated by al-Haakim and classed as saheeh by al-Albaani in al-Silsilah al-Saheehah (374).  

Fourthly:

 With regard to the life of the martyrs with their Lord, it is the life of al-Barzakh, where their Lord honours them with the delights of Paradise, where their position varies according to their deeds and intentions in this world. 

Allaah says (interpretation of the meaning): 

“Think not of those as dead who are killed in the way of Allaah. Nay, they are alive, with their Lord, and they have provision.

170. They rejoice in what Allaah has bestowed upon them of His Bounty and rejoice for the sake of those who have not yet joined them, but are left behind (not yet martyred) that on them no fear shall come, nor shall they grieve.

171. They rejoice in a grace and a bounty from Allaah, and that Allaah will not waste the reward of the believers”

[Aal ‘Imraan 3:169-171] 

“And say not of those who are killed in the way of Allaah, ‘They are dead.’ Nay, they are living, but you perceive (it) not”

[al-Baqarah 2:154]

Shaykh Ibn ‘Uthaymeen said: 

What is meant is that they are alive with their Lord, as it says in the verse from Aal ‘Imraan, but it is the life of al-barzakh and we do not know how it is. They have no need for food, drink or air, hence Allaah says “but you perceive (it) not” i.e., you do not perceive that they are living, because it is the life of al-barzakh in the unseen. If Allaah had not told us about it we would have no knowledge of it. 

Another thing we learn from the verse is that the martyrs are alive, but it is the life of al-barzakh which is nothing like life in this world, rather it is better and greater, but we do not know how it is. End quote. 

Tafseer Soorat al-Baqarah (2/176, 177). 

Ibn Rajab al-Hanbali (may Allaah have mercy on him) said, under the heading: Chapter on the location of the souls of the dead in al-Barzakh: 

As for the martyrs, most of the scholars are of the view that they are in Paradise. There are many ahaadeeth which speak of that. 

In Saheeh Muslim (1887) it is narrated that Masrooq said: We asked ‘Abd-Allaah ibn Mas’ood about this verse: “Think not of those as dead who are killed in the way of Allaah . Nay, they are alive, with their Lord, and they have provision” [Aal ‘Imraan 3:169]. He said: We also asked about that, and he (the Prophet (peace and blessings of Allaah be upon him)) said: “Their souls are in the crops of green birds, which have lamps hanging from the Throne, and they roam freely wherever they want in Paradise, then they return to those lamps…” 

Imam Ahmad, Abu Dawood and al-Haakim narrated, in a report that was classed as hasan by al-Albaani in Saheeh al-Targheeb (1379), from Sa’eed ibn Jubayr, that Ibn ‘Abbaas said: The Messenger of Allaah (peace and blessings of Allaah be upon him) said: “When your brethren were slain at Uhud, your Lord put their souls in the crops of green birds that go to the rivers of Paradise and eat of its fruits, then they go back to lamps of gold that are hanging in the shade of the Throne. When they find their food and drink and abode they said: Who will convey to our brethren that we are alive in Paradise and receiving provision, so that they will not give up fighting or turn away from jihad? And Allaah said: I shall tell them about you. Then Allaah, may He be exalted, revealed the verse: ‘Think not of those as dead who are killed in the way of Allaah . Nay, they are alive, with their Lord, and they have provision’ [Aal ‘Imraan 3:169].” 

Al-Tirmidhi and al-Haakim narrated, in a report that was classed as saheeh by al-Albaani in Saheeh al-Targheeb (13762) from Ibn ‘Abbaas that the Prophet (peace and blessings of Allaah be upon him) said: “I saw Ja’far ibn Abi Taalib as an angel flying in Paradise with the angels, with two wings.” End quote. 

Ahwaal al-Quboor (p. 92-104). 

Fifthly: 

With regard to asking the ruler for permission for jihad, this has been discussed in the answer to question no. 69746. If the kuffaar attack the Muslims, then jihad becomes an individual obligation (fard ‘ayn) in which case the permission of the ruler is no longer a condition. 

As for jihad with the aim of conquest and spreading Islam, the permission of the ruler is essential. 

And Allaah knows best.