noun
idiom; set phrase; idiomatic phrase
A fixed expression whose meaning cannot be deduced from the literal meanings of its parts. In Japanese linguistics, 慣用句 is often contrasted with ことわざ (proverb) and 四字熟語 (four-character compound).
「油を売る」は慣用句で、「時間を無駄にする」という意味です。
"Abura o uru" is an idiom meaning "to waste time."
日本語の慣用句を覚えるのは難しいですが、面白いです。
Learning Japanese idioms is difficult but interesting.