Originated in car culture to describe people who take Japanese economy cars and make them look like they're from The Fast And The Furious while doing nothing to improve actual performance.

Ricing is the name for extensively customizing your environment. Usually your desktop environment or your window manager or both.

Ricers are people who spend unreasonable amounts of time tweaking their OS to create something somewhat pretty but very often wildly impractical for any actual real world usage of a computer. Anime girls and drawings of japanese landscapes are usually involved.

synonym for theming, iirc