A cadetship is essentially full time employment for a university student, on the condition they study a degree relavent to their employment. The student benefits through gaining skills and experience in the workplace, and employers are able to train students in the field to suit the roles they need.
It's a great opportunity, because it puts you several years ahead career wise, of students who do not start relevant full time employment before finishing their degree, helps you really develop and grow into a work environment, can give you the practical element your studies lack, and most (obviously) importantly for all the high school kids who apply for these roles, you get paid a very good salary for somebody with no experience! -
credit to ilikecats