APS may stand for a number of different things, so it would be easier to give your question an accurate answer if you could explain the context where you heard it. However there are a few possibilities:
It could stand for the American Physical Society, which is an organisation that tries to spread knowledge of physics and support work in this area of science. In a UK context it could also mean the Association for Project Safety - this is an organisation that helps people and businesses conform to and understand health and safety legislation, especially in the construction industry. It's possible to join this organisation, receive training and certification etc if you work in an industry where health and safety is important.
In education it can also mean the Assisted Places Scheme, which was set up to help bright children from poor families study in independent schools with financial assistance.
If none of these is the right answer, please try asking again and giving the context - I'm sure someone will be able to help you.