Slip between the sheets? (7)
I believe the answer is:
erratum
'slip' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for erratum that I've seen before include "something wrong?" , "Mistake by Latin scholar" , "Printer's mistake" , "mistake in text" , "Mistake in book, etc" .)