A secular state is a concept of secularism, whereby a state or country purports to be officially neutral in matters of religion, supporting neither religion nor irreligion.
A secular state also claims to treat all its citizens equally regardless of religion, and claims to avoid preferential treatment for a citizen from a particular religion/nonreligion over other religions/nonreligion.
Secular states do not have a state religion (established religion) or equivalent, although the absence of a state religion does not necessarily mean that a state is fully secular; however, a true secular state should steadfastly maintain national governance without influence from religious factions; i.e. Separation of church and state.
Source from Wikipedia