Wiktionary
p60
n. (context UK Ireland English) The end-of-year tax certificate given to each employee by their employer.
Wikipedia
P60
In the UK and Ireland, a P60 (End of Year Certificate) is a statement issued to taxpayers at the end of a tax year. It is important a taxpayer does not destroy the P60 forms issued to them, as they form a vital part of the proof that tax has been paid.