Ancap is short for anarcho-capitalist. Ancaps disdain “statists” and favor markets unrestrained by rules and regulations.
Here’s a very readable blog post that helps give a sense of some of the ideas in play. It’s very interesting to read ancap philosophy, though useful to bear in mind that any one purported ancap can’t be assumed to represent the views of all others using that label. For example, so far I have found ancap sources that praise Ludwig Mises’ economic theory, another that calls him a “proto-ancap”, and others that lump him into a list of ‘misguided’ Libertarians, and so on.