English collocations are a natural combination of words closely affiliated with each other.
Some examples are "pay attention", "fast food", "make an effort", and "powerful engine".
Skilled users of the language can produce effects such as humor by varying the normal patterns of collocation.
Others are more open, where different words might be used to give the same meaning, as an example keep to or stick to the rules.
Idioms are collection of words in a fixed order that have a sense that cannot be guessed by knowing the meaning of the individual vocabularies.