[WR] Speedruns
Likewise, "PB" stands for Personal Best, the runner's best run/personal record
While we are at it, I'll also mention that "TAS" means "Tool Assisted Speedrun", which means the run wasn't made by a human being using a controller, but rather the inputs were pre-recorded and then played using a tool to get a theoretical perfect run (usually impossible for a human to replicate).
Not to confuse "TAS" with "TRASH", since those are just my runs. :P
Edited by the author
I've usually seen UWR to mean "Uncontested World Record" (i.e. "I'm the only schmuck who's ever run this game").