Question

What does idiom mean

Answer 1

Idiom is an expression whose meaning is different from the meaning of its individual words for example:

Piece of cake:

The meaning of this isn't self explanatory (literal) because the words aren't at all connected to the meaning. The meaning of this often used term means easy or simple.

Answer 2

A group of words established by usage as having a meaning not deducible from those of the individual words

OR

A characteristic mode of expression in music or art.