It’s complicated.
The terms "secular" and "secularism" have a variety of contradictory definitions. The two most significant ones as they relate to the government have quite different definitions, while a third term that pertains to private persons is also available:
1) Secularism as Governmental Non-Interference in Religious Matters: This definition of secularism refers to a government that actively refrains from regulating, controlling, supporting, or promoting religion or, if it does, does so regardless of religion and does so with strict scrutiny. This is the way that most Americans and Europeans understand the term secularism. According to this theory, the state and religion move through society like ships in the night, trying their best to avoid colliding.
2) Secularism as Direct Control and Delimitation of Religious Matters: This definition of secularism is most closely associated with Communism and some authoritarian governments in Asia, such as Atatürk's Turkey, France in the 1790s, and Mexico after the Revolution in 1917. Many characteristics of a theocracy are actually adopted by this kind of nation, including the effective inhibition, regulation, and control of all other religions and the promotion of one religion or ideology over all others. Just so happens to be non-religion, which is endorsed as "religion." As a result, these nations often have religious ministries to "manage" the other religions, and their legal framework severely weakens the state's religious institutions.
3) Secularism as a Personal Decision to Live Irreligiously: Atheists and agnostics have started employing euphemisms to express their attitude toward religion because the term "atheism" has been tarnished in a lot of contexts. These phrases, such as "humanist," "ethical culturalist," "bright," and "secularist," have certain meanings but do not literally indicate "atheist." However, since they don't offend as many people as atheism, they can successfully replace it.
Thank you,
Eddie