Masters courses (MA, MSc etc) are generally one-year full-time (or two-year part-time) taught courses. They can be either a continuation of your academic studies or a preparation for a specific careers, e.g. journalism, personnel management and IT.
Diploma or Certificate Courses are nearly always training for a specific career, e.g. teaching, social work etc.
Degree courses HND students may be seeking to take a shortened, related degree course.
Medical and related courses Graduates can train for a wide range of medical and related careers. There are new accelerated degree courses in medicine as well as shortened courses in other areas such as dietetics, nursing and speech therapy etc. Funding for some medically related courses is available even if you have already studied for a degree.
PhD the best known research qualification, a PhD will take at least three years to complete full-time and up to six years part-time. Assessment involves a written thesis and an oral exam (viva).
Other research qualifications include MPhil and MRes. These qualifications can be taken as a preparation for a PhD.