A set phrase or expression whose meaning is not predictable from the individual words; used in linguistic and everyday contexts.
"Abura o uru" is one of the Japanese idiomatic phrases.
Learning idiomatic phrases makes your conversation more natural.
慣用句 is a more common synonym with the same meaning; 慣用語句 is slightly more formal or technical.
イディオム is a loanword from English, often used in linguistic contexts, while 慣用語句 is the native Japanese term.
Compound of 慣用 (customary use) and 語句 (words and phrases).