What is A1, A2 etc?

Maybe it's just something that doesn't exist in my country, or my part of the industry (national news) but I've been various roles in broadcast for over a decade now, field ops, sat ops, master control room, support etc. Never heard anyone refer to someone as A2 or similar yet I see it mentioned here all the time like it's common knowledge so I'm guessing ive just managed to precisely thread my career to avoid this terminology.

Can someone give me a breakdown of these roles and what they entail? Is it more of an AV thing?