This is a great question, which already has some great answers. It was confusing to me at first too, and I fly in a very busy Tracon area. One thing that vexed me, and which you are sure to encounter, is that “approach” and “departure” are named for your phase in flight, not necessarily the frequency and controller you are on with. So, when departing you call “Norcal departure” and you might someone else refer to the same controller as “Norcal approach”. And yes, you guessed it, I am in northern California. I’ve also visited “SoCal approach” many times, and I love “Big Sky Approach”.
What else is out there?