Tarawih is the additional night prayer offered after Isha throughout the nights of Ramadan. The Prophet Muhammad prayed it in congregation for a few nights before stopping, fearing it might be mistaken for an obligation, and encouraged people afterward to pray it individually, promising that 'whoever prays at night through Ramadan out of faith and seeking reward, his previous sins will be forgiven' (Sahih al-Bukhari 2009). It was the caliph Umar ibn al-Khattab who later organized the community to pray tarawih together behind a single imam, a practice that has continued ever since. The number of rak'ahs is a matter of longstanding scholarly difference rather than fixed revelation: many mosques following Hanafi, Shafi'i, or Hanbali practice pray twenty rak'ahs (plus witr), based on reports from the early generations, while others — citing narrations about the Prophet's own night prayer — pray eight rak'ahs plus witr. Some Maliki communities historically prayed thirty-six. All of these are considered valid; what unites them is that tarawih is a voluntary (sunnah), not obligatory, prayer, and its true reward lies in sincerity and consistency rather than any particular rak'ah count.
Q&A · Prayer
What is tarawih prayer, and how many rak'ahs are prayed?
References
Sahih al-Bukhari 2009
Informational, not a personal fatwa. Consult a qualified scholar for rulings on your situation.