A Diploma is highly focused on industry specific skills in addition to theory, to prepare you for the working world. Most Diploma programs require you to complete an internship period before you can complete the program.
Courses offered in a diploma are very specific and are designed to provide you with an in-depth understanding and practical skills for that specific field. Hence it is important for you to have decided which bachelor’s degree and career you want to go into in the future.
A Foundation Program offers you a broader course structure compared to a Diploma. Foundation Programs also are however, quite centered around general fields, such as Science or Arts. So for example if you know you want to pursue a course in the science field in the future, but you are unsure about which specific course in the science field you want, a Foundation in Science would be a recommended study pathway for you.
That said, for students who want to pursue a specific course, there are also Foundation programs that are focused on specific courses such as Foundation in IT, Business or Architecture.