also: しょうよう
noun
trifling matter; small errand
Refers to a minor task or trivial business; often used in set phrases like 小用を足す (to run a small errand).
ちょっと小用で出かけてきます。
I'm going out for a small errand.
noun
Euphemistic or formal term for urination; often used in the phrase 小用を足す (to relieve oneself).
すみません、小用を足したいのですが。
Excuse me, I'd like to use the restroom.
Compound of 小 (small) and 用 (business, use). The urination sense is a euphemistic extension of 'small business'.