[Ninja_Bait]

Let's not get too crabby, guys.

I've always felt that "crab" holds the connotation that the robot is primarily meant to translate without rotating, much like a crab's motion. While there may be ways to make a crab drive rotate, it doesn't change the fact that the wheels almost always all point in the same direction and are meant to be used that way. (In this case, crab drive can also describe a control system.)

Swerve (and I've also heard vector drive) is the broader definition where the wheels actually can have different orientations relative to each other. That allows a wider variety of motions that a crab drive might struggle to achieve.

Honestly, though, it's just finicky semantics. We could also call them all "powered office chair caster wheel drives" but that would be lame. They're all basically built from the same idea, and the name doesn't matter as long as you're specific enough to differentiate the mechanism.