"Marxism" refers to a theory of the relationship between social classes and the economy. Communism, on the other hand, is a revolutionary political movement that actively seeks to change society. There is plenty of overlap, but not all Marxists would call themselves communists. Economists and sociologists may use Marxist theory as a method of analyzing trends and current events, but that doesn't necessarily mean they advocate for the abolition of private property or for any other communist principles.