What is a swing shift.?

a work shift from mid-afternoon to around midnight, and the hours may very with different companies

It's a shift that swings, meaning it oscillates. For example, you might be on night shift or day shift. Here's the schedule for a single group on a 24/7 schedule at a local paper mill where I live, the d's mean days, the n's mean nights, the o's mean off...

nnnnoooodddonnnoooddddooooooo

They get to do this schedule because each shift is 12 hours. That's how they get the 7 days off every 28 days. There are 4 shifts in rotation (A, B, C, D) that overlap slightly. Not all swing shifts are like this. I'm just giving an example of how in most places what "swing shift" means. It basically means in most places that the shift changes hours of work and usually has a set schedule so the person is prepared.

With that said, I'm sure some people use the term differently.