There is no definition of this word in my dictionary. The free dictionary has this definition:

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.

And the thesaurus has this insightful quote:

“memes are the cultural counterpart of genes”

And a sample usage of the word:

The Top Internet Memes of 2009

Memes – definition of Memes by the Free Online Dictionary, Thesaurus and Encyclopedia.