what's the difference between a saying, a set phrase, an idiom and a collocation?
I'd like to know the difference between a saying, a set phrase, an idiom and a collocation. I'd be grateful if you could give me some examples.

Question

Answer

Saying: a well-known and wise statement made by famous people, which often has a meaning that is different from the simple meanings of the words it contains

Idiom: group of words in a fixed order forming an expression whose meaning is not predictable from the usual meanings of its constituent elements/words

set phrase : 
A common expression whose wording is not subject to variation.

collation ( collect ) it means  study and compare (texts, evidence