Communism is an eventual end goal, a classless, stateless society. Socialism is a system that aims to progress towards that goal.

These terms have become muddled due to social democrats dropping the pretense that they want to establish communism (early social democrats like Eduard Bernstein argued for using reformism to establish communism), while still holding on to the “socialist” label. So there are some people who would use “socialist” to describe social democracy and reformism while reserving “communism” for Marxist-Leninists. This is quite strange considering that it was called the USSR and not the USCR, but what are you gonna do?

Since it’s often controversial whether a state that claims to be socialist is actually aiming to establish communism, some people use the term AES or “actually existing socialism” to describe modern states that call themselves socialist, because, whether or not they are “truly socialist,” they bear enough similarities and are distinct enough to warrant having a term to describe them.