Win ye an amazing prize!

[Sweder]

'O' refers to 'Ordinary' and 'A' to 'Advanced'.
These 'levels' are/ were examinations in the UK school system by which pupils are/ were judged at the end of their school life. In my day (old duffer alert) the emphasis was on the examination itself. These days, under new fancy names such as GCSE (no idea what that stands for) course work accounts for a large percentage of the final grade, which does seem to be an altogether fairer method of assessment.

Results help to determine if you get into University/ college should you so desire. Also employers use these as a guide to your powers of study and application, as well as a grounding in subjects relevant to employment.

Os and As were available in a wide variety of subjects - the sciences, maths, english, history, geography, religious education, languages. These days the subjects have broader scope. My son is studying (loose use of the term), amongst others;
Physics, Chemistry, Biology, French, English & Maths along with more modern subjects such as ICT (Information & Communication Technology) and Digital Photography.
You can also opt for sports qualifications. Sport was always something you did in betwen lessons at my school. These days they are valued more highly (a good thing in my book). You can build a fairly sturdy adult education programme based on such varied subjects as Sporting Turf Management, Athletics, Golf (and golf course management), amongst many others.

None of this has tempted me back into the education system. However, should the subject of Fine Beer Development (and tasting) I may review my options.

Incidentally, an unrestricted Google for O and A levels reveals an altogether different and less savoury explanation. Decorum and respect for my fellow forumites prevents me from going into more detail here.