A metajoke is a joke that references itself as a joke.

Here's an example:

Or for all you scientists:

An engineer, a physicist and a mathematician find themselves in an

anecdote, indeed an anecdote quite similar to many that you have

no doubt already heard. After some observations and rough calculations



the engineer realizes the situation and starts laughing. A few

minutes later the physicist understands too and chuckles to himself

happily as he now has enough experimental evidence to publish a

paper. This leaves the mathematician somewhat perplexed, as he

had observed right away that he was the subject of an anecdote,

and deduced quite rapidly the presence of humour from similar

anecdotes, but considers this anecdote to be too trivial a corollary

to be significant, let alone funny. (Source)