What exactly are Live service games?

Everything I see about these types of games is about how they're ruining the industry and are mostly slop, but from my understanding, aren't they just primarily multiplayer games that run on servers? This is probably a stupid fucking question but where does a game stop being like CS2 or Fortnite and start being live service slop, unless those are both slop as well. Im definitely misunderstanding something in discussion regarding the subject.