According to meme theory, a meme is a meaningful unit of information within the context of a given culture. The term was originally coined by Richard Dawkins in his book The Selfish Gene in the mid 1970s. He derived it from the word "gene", which is a unit of hereditary information. In the book Dawkins proposed the idea that social information could change and propagate through a culture in a way similar to genes in a population of organisms.
The idea was subsequently developed to include such things as political philosophies, religions, even languages. These were named memeplexes, because they contain vast numbers of interacting memes.
Like genes, memes may be useful, negative or neutral. For example, political philosophies - or indeed any philosophies and religions - are also memes or memeplexes. It is clear that such memeplexes do not necessarily have to be beneficial to survive and propagate.
In terms of meme theory, language teaching methodologies are also memeplexes which will propagate through populations for their own benefit and not for the benefit of the organizations that carried them.
Many memes are small and humorous in nature. "All Your Base Are Belong to Us" was an early internet meme, and "lolcats" is a popular current meme.