Skimmers, flitters, hoppers, what's the difference?
I mean, seriously, what is
it? Trek literature uses 'em all, and one could all things like crawlers and rollers. Quite possibly, there's a range of vehicles in use in the Trek universe with distinct means of motion, and these terms are massively more descriptive than the rather incomprehensible "car" or "tank" or "copter" or "plane"... A skimmer would be one of those things seen flying on the Cambridge lawn in "AGT", obviously.
Or then they are just different names for the same thing. Like First Officer and Executive Officer. Although in both cases, that would be quite unsatisfactory.