What is the definition of bid’ah? What is the ruling on doing more rak’ahs in Taraaweeh?

Praise be to Allaah. 

The root of the word bid’ah in Arabic means
initiating something without any precedent. For example, Allaah says
(interpretation of the meaning):

“The
Originator of the heavens and the earth…” [al-Baqarah 2:117]

 In the terminology of sharee’ah, bid’ah means
something that has been introduced into the religion of Allaah that has no
general or specific basis to support it.

 For example, the innovated adhkaar (dhikr) such
as saying the name of Allaah on its own (“Allaah…Allaah… Allaah”)
or the pronoun (“Hu… Hu… Hu…”, meaning “He… He… He…”).
This is a new thing that has been innovated in the religion, intended as
worship of Allaah, but there is no evidence for this, either specific or
general… so it is bid’ah.

 With regard to praying more than 8 rak’ahs in
Taraweeh, the Sunnah as reported in the saheeh ahaadeeth, and as the
Prophet
(peace and blessings of Allaah be upon him) did regularly, is
to pray eleven rak’ahs at night. He used to pray eight rak’ahs (saying
Tasleem after each two rak’ahs in most cases), ending with two rak’ahs
of shaf’ and one rak’ah of witr.

 He sometimes prayed thirteen rak’ahs, as was
narrated in the hadeeth of ‘Aa’ishah and Ibn ‘Abbaas (may Allaah be
pleased with them both). Doing more than this is permitted, but it is not
Sunnah. What indicates that it is permissible is the saheeh hadeeth in
which the Prophet
(peace and blessings of Allaah be upon him) said:
“Night prayer is two by two” – meaning two rak’ahs by two
rak’ahs; he did not limit it to a set number. And Allaah knows best.