Answer: Suicide is when a person kills himself intentionally by whatever means. This is haraam and regarded as amongst the major sins, and likewise included in the general statement of Allaah (subhaanahu wa ta'aala):
"And whoever kills a believer intentionally, his recompense is Hell to abide therein, and the Wrath and the Curse of Allaah are upon him, and a great punishment is prepared for him." [Soorah an-Nisaa, (4):93]
And it is established from the Sunnah on the authority of the Prophet (sal-Allaahu `alayhe wa sallam) who said:
"Indeed, whoever (intentionally) kills himself, then certainly he will be punished in the Fire of Hell, wherein he shall dwell forever." [Bukhaaree (5778) and Muslim (109 and 110)]
In reality, the one who commits suicide, generally does so because of his desperate situation, either as a direct result of an act of Allaah or a human being. So you find him unable to cope with that which has afflicted him, and in actual fact he is like one who is calling for help from the scorching heat of the fire. So he has progressed from that which was tough (bad) to that which is worse. And if he was patient, then Allaah would have assisted him in dealing with the difficulty.