Simple Definition:

Diversity is the state or quality of being diverse [different or varied]. It refers to the inclusion and representation of people from various races, ethnicities, genders, religions, nationalities, abilities, and other characteristics, creating a rich and varied mix. For example, a diverse workplace may consist of employees from different countries, backgrounds, and cultures, as well as individuals with different skills and experiences.

Very Simple Definition:

Diversity means having different kinds of people. It means having people from different races, countries, cultures, and abilities all together. For example, a diverse group of friends can include people from different countries and who look different.