Tarawih Prayer is a special prayer Muslims perform only in the month of Ramadhan. It is a sunnah(optional) prayers, which means that it was Prophet Muhammad's (peace and blessings be upon him) practice and Muslims are encouraged to do likewise.
The word Tarawih comes from an Arabic word which means to rest and relax. The first Tarawih Prayer of Ramadhan will be performed the evening before the fast actually begins. The time for the prayer is from after 'Isha' prayer until dawn comes. Tarawih prayers are performed in any even amount of rak'ah, with the norm being 8 or 20 raka'ahs. It is preferable to perform the Witr Prayer of 1-3 rak'ahs after the completion of the Tarawih Prayer.
Tarawih Prayer can be performed at home, alone, in congregation, or at a mosque. In many mosques, one juz' of the Qur'an is recited each night in Tarawih. Thus performing Tarawih in the mosque imparts a special flavor to Ramadan, especially if one is able to do so every night and hear each juz' of the Qur'an recited during the month.
Abu Hurayrah narrated that the Messenger of Allah said,
"Whoever establishes prayers during the nights of Ramadan faithfully out of sincere faith and hoping to attain Allah's rewards (not for showing off), all his past sins will be forgiven."