Dirt, grime, or scum that accumulates on surfaces — e.g. dead skin (smegma/skin dirt), grease or limescale on objects.
お風呂で垢を落としてから寝たほうがさっぱりする。
You'll feel refreshed if you wash off the grime in the bath before going to bed.
歯ブラシを交換しないと、歯垢や垢がたまりやすい。
If you don't replace your toothbrush, plaque and grime can build up easily.
やかんの内側に付いた垢を落とすのは面倒だ。
Scrubbing the grime off the inside of a kettle is a hassle.