The word ‘jihad: جهاد’ is from the root ‘جهد’ which means ‘striving’.
‘Jihad’ and ‘qital’, which is also explained below, are confused most of the time.
Jihad is upholding and conveying the truth, the true religion, inspite of all difficulties because, the impact of truth on people cannot be compared to anything. The command of ‘jihad’ is found in the following verse in Qur’an:
فَلَا تُطِعِ الْكَافِرِينَ وَجَاهِدْهُمْ بِهِ جِهَادًا كَبِيرًا
“So do not obey the disbelievers, and strive against them with the Qur’an a great striving.” (Al-Furqan/The Criterion 25:52)
This is a bilateral strive. One side strives to suppress you, and you strive against them to reveal the truth, and convey the message of Qur’an. This is the essence of jihad.
The aim is not killing people; but killing the wrong belief inside the people, and saving them by telling the truth.
Let’s also see the following verse about jihad:
وَجَاهِدُوا فِي اللَّـهِ حَقَّ جِهَادِهِ هُوَ اجْتَبَاكُمْ وَمَا جَعَلَ عَلَيْكُمْ فِي الدِّينِ مِنْ حَرَجٍ مِلَّةَ أَبِيكُمْ إِبْرَاهِيمَ
“And strive (jaahadu) for Allah in a manner worthy of that striving. He has chosen you and has not placed upon you in the religion any difficulty. [It is] the religion of your father, Abraham.” (Al-Hajj/ The Pilgrimage 22:78)
We have not a single clue that Prophet Abraham (p.b.u.h.) ever fought against anyone. However, he strove against his people to withhold them from the religion and wrong beliefs of their ancestors. We know also from the verse 3:67 that the religion of Abraham was Islam, too. Considering the verse above, we can be sure that jihad is not equal to fighting, though it may include fighting when required. Its conditions are explained in the related texts below.
There also exists the command of fighting in the way of Allah, in the Qur’an.
‘Qital : قتال’ is from the root ‘قتل’ which means ‘fighting’.
Allah the Almighty commands to fight in His way, but not against everybody:
وَقَاتِلُوا فِي سَبِيلِ اللَّـهِ الَّذِينَ يُقَاتِلُونَكُمْ وَلَا تَعْتَدُوا إِنَّ اللَّـهَ لَا يُحِبُّ الْمُعْتَدِينَ
“Fight (qaatilu) in the way of Allah those who fight you, but do not transgress. Indeed, Allah does not like transgressors.” (Al-Baqarah/The Cow 2:190)
For further reference on fighting and battles of Prophet Muhammad (p.b.u.h.) see the following texts:
Relations with non-Muslims: http://www.islamandquran.org/?p=1201
Is Islam a religion of war, or peace?: http://www.islamandquran.org/?p=3670