This is the origin of the word as far as I know. Two opposing ramps originally used for BMXers, but now used by snow boarders, roller bladers, skateboards and others. See also quarter pipe.
I heard they're building a new half-pipe down at the park this summer. Let's try it out but I'm not down with wearing all of the armor they are going to require.
Due to the low center of mass of most dogs, people often think putting them on a skateboard and dropping them into a halfpipe would be a good idea. This could not be further from the truth, for anyone going down a halfpipe should wear the necessary equipment, and companies do not yet supply helmets to dogs. In conclusion, keep the dog off the halfpipe and stay safe.
Yo bro, you really shouldn't go out to that party during this pandemic.