Meta is a word which, like so many other things, we have the ancient Greeks to thank for. When they used it, meta meant “beyond,” “after,” or “behind.” The “beyond” sense of meta still lingers in words like metaphysics or meta-economy. But that’s still not the meta most of us come across today.
One of the more popular uses of meta today is for the meaning best described by the formula “meta-X equals X about X.” So, if we take the word “data” for our X, and add the prefix meta- to it, we get metadata, or “data about data.” A meta-text is a text about texts, metacognition is thinking about thinking, and a meta-joke is a joke about jokes.