Heterogeneous can be used to describe the diversity of nearly anything — populations, classrooms, collections. A heterogeneous array of immigrants passed through Ellis Island to help create the American "melting pot."
An easy way to remember the meaning of this word is that homo is the same and hetero is different. So, a homogeneous group of puppies might consist of apricot-colored poodles, while a heterogeneous group might consist of a hodgepodge of different pups ranging from dachshunds to dalmatians. Anytime you are confronted with a group whose members are not all similar to one another, you have an opportunity to trot out heterogeneous.