Hello there,
You can apply for your Diploma in any subject after your Class 10. After completing it, you will get your Diploma pass certificate. It is not your 12th pass certificate. With the diploma pass certificate, you can apply to other colleges for the relevant courses.

For example, after completing a 3year Diploma course in Engineering, one can apply for his/her B.tech degree. The person will get direct admission to 2nd year, with the Diploma Certificate.

Hope this answer helps you.
Good luck!!