Does anyone know what a speedrun is [WR]

It's shorthand for World Record.

Keeps video titles a little shorter, I guess.

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

I guess we could also mention "SoB" which stands for "Sum of Best" which is the cumulative time of all of the runner's best segments.

There's also sometime [TWR] = tied world record [FWR] = former world record [UWR] untied/unofficial world record (I've seen it mean both)

I've usually seen UWR to mean "Uncontested World Record" (i.e. "I'm the only schmuck who's ever run this game").