I always assumed you needed to be hidden to get advantage when attacking/disadvantage when being attacked, but after looking at the rules I'm fairly certain this is not the case. There's a chance I'm reading into it incorrectly, though.
For example, assume I have greater invisibility cast on myself. No matter how many attacks I make, or whether or not my enemy knows where I am (but can't actually see me), do I still have advantage to hit and they have disadvantage to hit me?
I think that's what's accurate. This would implicate that "Hidden" means "Enemies don't know where you are and think you could be anywhere", which changes my prior understanding of hiding drastically.
Am I correct on this?