Yeah, I think it changes pretty rapidly but the basics have been the same for some time.
-Power Distribution Board (PDB) of one kind or another (think separate board, or built into the Flight Controller are the two most popular)
-Flight Controller (FC) board of one kind of hardware architecture or another (think F3, F4, Arduino (KISS) etc, orAIO All In One, etc) and some kind of flight control software (think Race Flight, Beta Fight as the most popular)
-Electronic Speed Controller (ESC)
-Motors
-Receiver
Edit: To fly FPV we also need the camera and Video Transmiter (VTX) thingies and a VTX antenna of some kind... Duh, stupid me, I was thinking propulsion.
That's the basic big pieces that makes up the thingy that goes up in the air
Of course there are batteries and props but we wont consider those for the purposes of the basic quad.
There are a lot of variations out there, think 4 in 1 ESC's, or individual ESC's, that kind of thing, but they all have to do at least those 5 things somehow... and of course, some work better than others.
That's the take I've learned over the last 6 months anyway, I hope that helps a little.