We don't know...yet!
Marvel have not yet clarified what any or all of these terms mean for them.
Indeed Marvel haven't commented at all but rather the various creators, such as the Russo Brothers have used the terms but again, have failed to define them and in many cases used them interchangeably.
Anthony Russo: "Loki could absolutely still be alive in an alternate timeline."
Anthoy Russo: "In the movie, the Hulk is very explicit about what our rules are, which is you cannot change the present by altering the past. All you can do by going to the past — and for a character like Cap[tain America], living in the past — is create an alternate future. So this is a world in which alternate timelines exist."
Joe Russo: "The minute that Loki does something as dramatic as take the Space Stone, he creates a branched reality."
Given the, ahem, issues with in Captain America, Loki (and possibly others) in Endgame and the revelation that there are other Earths in Spider-Man: Far From Home this has yet to be explained.
It's likely that Phase 4 and forthcoming/proposed Disney+ productions (VandaVision, Loki series, Winter Soldier & Falcon series and What If? etc.) may explore this further.