A diploma is a document people receive when they graduate from a school or program. It is a symbol of academic success. You often see framed diplomas displayed in a doctor's office.
Are you working toward a diploma? Then you must be in school. People receive high school and college diplomas, which they usually receive during a graduation ceremony. You could also get a diploma for a shorter series of classes in something like pottery, skydiving, or marksmanship. Even a dog could get a diploma for passing obedience school. Any time someone gets a diploma, you can be sure they finished a course or program of learning.