Mother's knocked up top pancetta stuffing for meat (4)
I believe the answer is:
spam
'for meat' is the definition.
(Spam is an example)
'mother's knocked up top pancetta stuffing' is the wordplay.
'mother's' becomes 'ma's' (Ma is another word for mother or mum).
'knocked up' says the letters should be written backwards.
'top' says to take the initial letters.
'stuffing' indicates putting letters inside.
The first letter of 'pancetta' is 'p'.
'mas' reversed gives 'sam'.
'sam' going around 'p' is 'SPAM'.
(Other definitions for spam that I've seen before include "unwanted delivery" , "Tinned meat - unwanted email" , "Spiced ham" , "Send unsolicited mail" , "Food" .)