All-Mountain / Enduro
Still lots of pedaling up, down, and all around but the focus is on the "down," which usually includes more technical trails for the descents than XC does
It's all about going downhill and finding jumps, stunts, drops, etc to keep things spicy with a focus on riding style. An extreme example of freeriding is the Red Bull Rampage event
Again, all about going downhill and similar to freeriding but more emphasis on going fast. Speed and style but mostly just speed. I usually ride a lift or take a shuttle to the top.
Not always just on dirt but this usually refers to packs of jumps, bermed turns, pumping, and working towards maximum air time
Closely related to dirt jumping but usually done on dedicated BMX tracks or freestyle courses and on 20" or 24" wheeled bikes
Lots of pedaling up, down, and all around
The Belgians' idea of having a good time in the winter on their road bikes. CX is usually done on drop-bar bikes and includes riding on and off road, dismounting to jump hurdles or run up steep hills or stairs, and usually includes sprints and hard efforts that make you feel like you are turning yourself inside out
Gravel Grinding / Bike Packing / Touring / Road Riding
These are all different disciplines but basically center around riding for miles on bikes with little to no suspension and on skinnier tires than mountain bikes typically have. Lots of saddle time!
Opting to be your own engine rather than using fossil fuels to get around