Passes are pieces of paper! (5)
I believe the answer is:
slips
'passes' is the definition.
The definition and answer can be both acts as well as being plural nouns.
Maybe there's an association between them I don't understand?
'pieces of paper' is the wordplay.
I cannot really understand how this works, but
'pieces' could be 'lips' (lip is a kind of piece) and 'lips' is present in the answer.
A single letter 's' remains which might be clued in a way I don't understand.
This explanation may well be incorrect...
'are' is the link.
Can you help me to learn more?
(Other definitions for slips that I've seen before include "They try to catch you" , "errors" .)