Bull Pen Catching

In MLB, the bullpen catchers are considered coaches I believe. Ocasionally one of the catchers on the roster will go down and catch in the bullpen, but the majority of it that you'll see while at a game is done by someone not on the active roster.

College they probably carry 3-4 catchers depending. The 3rd catcher is normally doing bullpen duty and maybe the 4th if they have one. The second might go down there if they have to warm up more than one. From what I've seen the starting catcher MIGHT go down right before a game, but practices probably don't see him in the bullpen a whole lot.

High school is just kind of varies..

There is a 'bullpen catcher' job title in the majors; in the minors, the non-starting catcher stays in the bullpen, but the starting catcher warms up the starting pitcher so that they get on the same page (the same is generally true in college).