Simplest answer is it's a Serato DJ Plugin that enables you to record and playback "Que" sequences as you're performing.
I don't have DVS, but since you're just reading time code, I see no reason it wouldn't work with it - but that's probably a better
question for the Serato Forum.
Handinon explained it well. It's basically a way to make edits, without having to actually edit the song file.
Lots of DJs make edits to chop a track down to the way they want to play it. Maybe the build up is too long, or the breakdown is too long, or the intro could be cooler incorporating another chunk of the song. You can record that sequence that you want, and then play it back on command without having to edit the track itself.