The adjective heterogenous is a somewhat comparative word, suggesting that two or more things are unlike in substance or nature, as in a heterogenous mixture containing two substances that do not totally combine, like oil and water.
We can see the roots of heterogenous in the Greek combination of heteros, meaning "other," and genos, meaning "a kind." So heterogenous means "other kind." The United States, as a melting pot of cultures, contains a heterogenous population. Note that while this spelling is acceptable, the word is more correctly spelled heterogeneous, with the ending adding an "e" before the ous.