This common name refers to only one class.
These are pretty much always called Fishes.
Baitfish are a very important part of the diet of large trout, in both streams and rivers. Some streamer fishermen believe matching a particular species of baitfish may give an edge, just as hatch-matching helps fool insectivorous fish.
The specific properties of baitfish vary so widely that, given the relative unimportance of their differences, I have not yet put aside the time to write about them.
On this site, I the whole fishes section is deliberately incomplete. It's focused on possible prey for trout, and other taxa are left off the lists. I haven't put as much time into this fish section as I have into the insects, but I will start adding some good closeups of more baitfish species soon.