Secularity is the state of being separate from religion, or of not being exclusively allied with or against any particular religion. It separates the power of the state and religion.
By the 42nd Amendment in 1976, the term "Secular" was also incorporated in the Preamble. There is no difference of religion i.e. all religion are equally respected and moreover, there is no state religion. All the citizens of India are allowed to profess, practice and propagate any religion.