As Cameron says, it's a joke - a play on words based on the fact that 'eggs' and 'ex' sound the same. Here's how you might use it: "How was your omelette?" "Very good indeed. In fact, it was egg-ceptionally good. Egg-cellent, in fact! " (Thanks for the egg-stra joke, Bob)

egg-cellent question! :)

I assume you are talking about a joke referring to the word exceptionally. It is a play on words because the word "egg" sounds similar to the prefix "ex".