I found this on the Evolve Politics site, apparently quoting from the ONS, Gracesgran:
"The employed are defined as those aged 16 or over, who are in employment if they did at least one hour of work in the reference week (as an employee, as self-employed, as unpaid workers in a family business, or as participants in government-supported training schemes), and those who had a job that they were temporarily away from (for example, if they are on holiday)."
Evolve goes on to say:
"Secondly, this is how they define unemployment:
"The unemployed are defined as those aged 16 or over, who are without work, have actively sought work in the last four weeks and are available to start work in the next two weeks; or are out of work but have found a job and are waiting to start it within the next two weeks."
"And then there is the last category – the ‘economically inactive’, which is defined by the ONS as:
"those aged 16 or over who are neither in employment nor unemployed. This group includes, for example, all those who are looking after a home or family, have a long-term illness or disability which prevents them working, or are retired."