According to Wikipedia:
An Internet meme ( /ˈmiːm/ meem) is a concept that spreads via the Internet. The word meme was coined by Richard Dawkins for his 1976 bookThe Selfish Gene, although his concept refers to a much broader category of cultural information.
Read more about what Wikipedia says about internet memes here.
A meme you might be familiar with is the ‘keep calm and…’ poster which has been remixed by others and spread around the internet and indeed can be bought emblazoned on merchandise – for example, I have a mug that says ‘Keep Calm and Rule Britannia’. So a meme is a concept or idea that people then change and adapt to make a point or, usually, a joke.
If you’re unsure about a picture you see with a caption on it the best place to go first is here: http://knowyourmeme.com/
Take a look at this infographic here for further explanations.
To create a meme and see others that people have made visit: http://memegenerator.net/. This is where we create the memes on this site.