Anti-capitalism (sometimes abbreviated Anti-cap) is a political ideology and movement encompassing a variety of attitudes and ideas that oppose capitalism. In this sense, anti-capitalists are those who wish to replace capitalism with another type of economic system, usually some form of socialism. This should not be confused for social democracy that superficially espouses 'anti-capitalism' but advocates for less 'extreme' capitalism by use of a welfare state.
Anti-capitalism can emerge in a variety of movements that are not communist or Marxist in general but other movements like anarchism. The only common strand they have is their tendency to oppose capital and the effects of such a system.