- What is Bi'dah? - Innovation in religion

Whatever action is not proven by the Prophet is known as Bi'dah (innovation in religion). 

There are two types of Bi'dah, Bi'dat-e-Hasana (Good) and Bi'dat-e-Sayyia (Evil). 

Bi'dat-e-Hasana is that where it is not against or contradicts a Sunnat. Like, to build mosques from concrete or bricks, or to write the Qur'an in golden letters, To perform intention with the tongue, to learn knowledge of Kalaam, Sarf and Nahoo (Arabic grammar), to learn knowledge of astronomy, to learn knowledge of pure mathematics or trigonometry or to preach all this knowledge. It is also Bi'dat-e-Hasana to build education institutes (Madressas) like we do today, to perform functions as we do today and to five out certificates and perform occasions like 'Dastaar Bandi' etc. There are thousands of things like these that were not present during the time of the Prophet. They are all Bi'dat-e-Hasana and in fact some are now necessary (Wajib), like to pray Tarawih as 'Umar (may Allah be pleased with him) stated "Ne'matil Bidatoo Haadhihee." meaning this is a good Bi'dat. 

Bi'dat Siyyia Qabiha is that innovation that is against a Sunnat or contradicts a Sunnat and this is either Makrooh (disliked) or Haram (strictly forbidden).