What is istikhara ?

Istikhara" means to seek goodness, from Allah (Exalted is He), meaning when one intends to do an important task they do istikhara before the task.

 The one who does the istikhara is as if they request Allah Almighty that, O the Knower of Unseen (Exalted is He) guide me if this task is better for me or not? 

According to Bukhari, Volume 2, Book 21, Number 263:

 Narrated Jabir bin 'Abdullah :The Prophet (Sallal Laho Alaihi Wasallam) used to teach us the way of doing Istikhara, in all matters as he taught us the Suras of the Quran. 

He said, "If anyone of you thinks of doing any job he should offer a two Rakat prayer other than the compulsory ones and say (after the prayer):