A definition from dictionary.com:
"division into two mutually exclusive, opposed, or contradictory groups"
An illustrated example:

Cover by Margot Austin, October 1956 Jack and Jill Magazine
...meanderings of a children's bookseller on the subject of books, book collecting and running an out of print book business in the internet age.
a cultural item that is transmitted by repetition in a manner analogous to the biological transmission of genes.
a unit of cultural information, such as a cultural practice or idea, that is transmitted verbally or by repeated action from one mind to another.