1 : the quality or state of having many different forms, types, ideas, etc.
(noncount)
The island has more diversity in plant life than other islands nearby.
biological/genetic/linguistic diversity
There was some diversity of opinion about what should be done. (=people had different opinions about what should be done)
(count) — usually singular
The area has a great diversity (=variety) of birds.
She has a wide diversity of interests. (=she has many different interests)
2 : the state of having people who are different races or who have different cultures in a group or organization
(noncount)
The city is known for its cultural/ethnic diversity.
The school aims for diversity in its student population.
(count) — usually singular
There is a greater diversity in the city’s population now.