Words that sound good together, typically something that a native english speaker would easily understand because the phrase is used a lot. Context is key to understanding these phrases.
Exp 1. "Strong tea" is a collocation

Exp 2. "No real solutions" refers to an equation
Exp 3. There is a difference between using "impossible" and "undefined"
by concept not format October 20, 2019
a hard frost is an example where the Word collocation doesnt apear in, but is the definition of lol Xd
by owl with a gasmask February 5, 2018
You will probably never need to know what collocations are, but school still teaches you what it is for no reason other then to just waste your time.

Also collocations are just words that fit together, like a hard frost
Teacher: Okay class, today we are going to learn about collocations!
Student: Will there ever be a situation in life where we need to know what collocations are?
Teacher: ...
Teacher: No.
by owl with a gasmask April 6, 2018