There is definitely a difference, and they are not interchangeable. I’ll let other people chime in with a rigorous definition for communism, but at a minimum, it must have abolished the state and social classes entirely. So one could say that communism is at the very end of the road, and the various flavors of socialism are the routes to get there.

Various flavors of socialism? Yes, I’ve written an earlier comment about that, and another one here. In brief, there are many ways to move beyond capitalism.