Okay, so the first thing to recognise is that terminology in left wing theory can be super confusing and the same words can be used to mean different things at different times or in different places, or sometimes in the same place at the same time.

Communism however in modern usage is fairly straightforward as it is used almost exclusively as it is defined in conventional Marxist doctrine(and yes there are many branches of Marxism).

That said big C Communism means a state of being that is achieved as the end point of societal evolution where there is no state, the means of production is controlled by the community and the needs of all are met.

In conventional Marxist thought the way of achieving this is through a transitional stage of socialism where the means of production is controlled by a “Vanguard” state. Many states in history have claimed to be communist in ideology(they are working towards this stateless utopia) but none have claimed to have achieved communism, only to be in the process of transitioning to it.

To all the leftist theory heads out there, don’t at me, I know this is a huge oversimplification, it is deliberate for someone who is obviously new to this.