The name stands for British Age Group Category and is a way of measuring and comparing the performance of swimmers across a range of different events and age groups.  The intention of the ASA is to encourage younger swimmers to compete in a wide range of events and not specialise in a particular stroke and distance too early.  When a swimmer competes in a BAGCAT event their time is converted into points that take into account not only their time but also the stroke, their age, sex and various correction factors.

Further information and a calculator can be found at the following;

ASA Technical Swimming Committee statement on BAGCAT point scoring from 2010