A mem is memory transmited from one mind to another.
When an animal learns by imitating another animal of the same kind, instead of just following his geneticaly coded instincts, a mem is transported.
The older animals get and the more often they meet to learn from each other the more memes develop.
The ability of coding, storing and reading information on media outside ones mind enables the forming of cults and religion.
Cultures are based on memes.
Memes are like a virtual, medium intependent, virus.
Different definitions of meme generally agree, very roughly, that a meme consists of some sort of a self-propagating unit of cultural evolution having a resemblance to the gene (the unit of genetics).
Examples might include thoughts, ideas, theories, practices, habits, songs, dances and moods in addition to concepts such as religion, law, race...