Unusual mathematical terms

I've always liked 'abstract nonsense'.

To quote wikipedia:

Note that referring to an argument as "abstract nonsense" is not supposed to be a derogatory expression, and is actually often a compliment regarding the generality and sophistication of the argument.

Complex theorems often use simple, illustrative names.
Ham Sandwich Theorem
No Free Lunch Theorem
Ugly Duckling Theorem

Some are named by the scenario they are describing
Birthday Attack
Doomsday Argument

Other by the accompanying real-life events
Happy Ending Problem

and finally the top 10 Dirty Mathematics from Spikedmath (slightly edited to take up less space)
A Survey on Cox Rings
Cox-Zucker machine