Bidah linguistically means innovation, and according to the Islamic terminology is anything that innovated and not mentioned in the Qur'an or in Hadeeth. The Islamic scholars divided the Bidah into 2 categories: Bidatul Huda Bidatul Dalalah. This is based on Hadeeth of the Prophet Muhammad, may Allah increase his honor,
Man sanna fil Islami sunnatan hasanatan falahu ajruha a ajru man ^amila biha min Ba^dih la yanqusu min ujurihim shay', wa man sana fil Islami sunatan sayi'atan falahu wizruha wa wizru man ^amila biha min ba^dihi la yanqusu min awzarihim shay'.
The Hadeeth is by Jarir Ibni Abdillahil-Bajaliyy, narrated by Muslim.
Consequently, to label all bidah as somthing bad is not correct. Any bidah that contradicts the Shariah and the Islamic teachings is bad with no doubt, nonetheless, any bidah that is consistent with the shariah is a good and rewardable bidah.