The ‘graduate employability’ statistic mirrors the ‘Graduate Prospects’ measure as defined by The Times and The Sunday Times Good University Guide. It is defined as “the proportion of UK domiciled, full-time, first degree graduates who say they entered professional employment or graduate-level further study as a percentage of all those who are working, studying, or seeking work.”
The population is not quite the same as ‘employability’ because graduates who are due to start a job within a month are considered ‘unemployed’ in the employability calculation, but are excluded from the graduate employability calculation. You can therefore sometimes get a higher percentage rate for ‘graduate employability’ than for ‘employability’.