What does it mean to be secular?
Secular means different things to different people.
In his book, How (not) to be secular, James K.A. Smith gives three distinct definitions of "secular".
"the earthly plane of domestic life"
This is the "classical" or "historical" definition, and distinguishes the secular from the sacred, i.e. the domain of priests. "butchers, bakers, and candlestick makers carry out "secular" work. To early reformers such as Luther this was positive. There was to be no distinction between the sacred and the secular.
"the areligious - neutral, unbiased, objective"
This is a "modern" definition. It is particularly used in claims that the "public square", i.e. politics and public debate should be "free" from discussions about religion or religious values and perspectives.
This is the notion of Charles Taylor, who in A Secular Age, says it
“consists, among other things, of a move from a society where belief in God is unchallenged and indeed unproblematic to one in which it is understood to be one option among others, and frequently not the easiest to embrace”.