They're interchangable technobabble terms. According to "Parallels" there's an alternate reality for every possible outcome of every event, anywhere, ever. That covers everything from "Mirror, Mirror" to "Yesterday's Enterprise" to "Non Sequiter" to "Endgame" to "Shockwave" to STXI.Non sequitor was about "timestreams", not timelines and it was about changing space more so than time. Space got replaced rather time plit or frayed, even is time was the causal factor.
Parallels was about Quanutm realities. Entire Universes that just happened to be different more so that they had diverged form one another.