A petition is a request to do something, most commonly addressed to a government official or public entity.
In the colloquial sense, a petition is a document addressed to some official and signed by numerous individuals. A petition may be oral rather than written, or may be transmitted via the Internet.
In some countries (including India), there are particular committees devoted to addressal of petitions. In India, there is the Committee on Petitions, which does this task. The details can be found here.
Besides, there can be several informal petitions, in the form of online petitions or street rallies. As of March 2018, these do not have provide any legal obligations for the Parliament to initiate the change. These can only be useful in spreading awareness, and showing participation. For actual change, a written petition is required to be submitted to the concerned authoritites. (See link above.)