GCSE stands for General Certificate of Secondary Education. These are the courses that students follow during their last few years of compulsory schooling, usually between the ages of 14 and 16. Students often take around eight GCSEs (sometimes more and sometimes fewer depending on their ability and the policy of the school). Core subjects, like Maths, English and Science, must be studied.
GCSEs are usually two-year courses which will generally be assessed by written examinations at the end of the course (in May or June). Grading is from 9 (highest) to 1 (lowest) as opposed to the old A* to G system. It may be possible to re-sit certain subjects (for example, Maths and English) in November.
After completing their GCSE exams, students who wish to go to university generally study A levels. As a rule of thumb, A level colleges and universities require at least 5 GCSEs.