In the UK, you have to apply for university through UCAS. For almost all subjects you can only apply to 5 courses. However, for medicine this is limited to 4, and your fifth choice must be something different, but often it is a related subject e.g. biomedical sciences. So for any year you can apply to a maximum of 5 unis in the UK, of which only 4 will be medical courses. You can also apply to a university abroad if you want to, and this is not through UCAS.