[1] In the specific case of social networks, assortative mixing is also known as homophily.
The rarer disassortative mixing is a bias in favor of connections between dissimilar nodes.
In social networks, for example, individuals commonly choose to associate with others of similar age, nationality, location, race, income, educational level, religion, or language as themselves.
[2] In networks of sexual contact, the same biases are observed, but mixing is also disassortative by gender – most partnerships are between individuals of opposite sex.
Assortative mixing can have effects, for example, on the spread of disease: if individuals have contact primarily with other members of the same population groups, then diseases will spread primarily within those groups.