Statutory Residence Tests - what qualifies as 'work'?

The SRT pages of the HMRC website make regular reference to the term 'work'. Yet nowhere can I find a definition of the term. Does it mean work for which remuneration was made as part of an employment contract of some kind? Or does it include unpaid or volunteer work? Does non-specific work as a director of a company count, if no renumeration is received? Any guidance appreciated

Hi,
Definitions are outlined at:
RDRM11740 - Residence: The SRT: Days spent in the UK: Work for the purpose of the SRT
Thankyou