Degree and Diploma are both academics awards issued educational institutions which show that the recipient has successfully completed a course of study. The above little explanation does not mean both awards are the same. In most countries of the world, the period of time to be used to complete a degree program is usually around 3-4 years, while it can take between 1-2 years for someone to complete a diploma course.
In fact, some diploma courses can be completed in less than a year. Unlike a degree that can only be issued by a well recognized university, a diploma can be issued by private institutions, vocational institutions, etc. When studying a degree program, you will not be limited to your course of study, but you will have chances to study more about other related courses.
In contrast, a diploma program is very narrow in scope since you will be trained only on your preferred course of study.