How it defines (a) education, (b) training and (c) employment in terms of positive destinations.

Definitions of destinations used in the Scottish Government's positive destination statistics can be found in the background notes of the relevant publications, for example in section 7.4.1 of the 2021/22 Summary Statistics for Attainment and Initial Leaver destinations publication . This includes definitions for Higher Education, Further Education, Training and Employment. Note that those still attending education at school are not included in these statistics. The definitions are reproduced below.
Higher Education: includes leavers following Higher National Diploma (HND) or Higher National Certificate (HNC) courses, degree courses, courses for the education and training of teachers and higher level courses for professional qualifications. It includes programmes at a level higher than the standard of the National Qualifications, i.e. above SCQF Level 7. Leavers with a deferred, unconditional place in higher education have also been included in this category.
Further Education: includes leavers undertaking full-time education which is not higher education and who are no longer on a school roll. This may include National Qualifications.
Training: includes leavers who are on a training course and in receipt of an allowance or grant. It also includes leavers who are on local authority or third sector funded training programmes that are in receipt of a training allowance or those participating in Community Jobs Scotland.
Employment: includes those who consider themselves to be employed and in receipt of payment from their employers. It includes young people undertaking training in employment through national training programmes such as Modern Apprenticeships and Graduate Apprenticeships.