Examples of unexpected names of concepts in mathematics

Question

I was wondering around wikipedia and I found two concepts called "Monstrous moonshine" i.e.

In mathematics, monstrous moonshine, or moonshine theory, is the unexpected connection between the monster group M and modular functions, in particular, the j function. The term was coined by John Conway and Simon P. Norton in 1979.

And then as a consequence "Monster group" i.e.

In the area of modern algebra known as group theory, the Monster group M (also known as the Fischer–Griess Monster, or the Friendly Giant) is the largest sporadic simple group,

So without real need of understanding those concepts, do you guys know any more such concepts with unexpected names? Obviously word "unexpected" has a very subjective meaning so I will leave it for you to decide what such name is. This is purely recreational question, I hope it is fine to post it.

Answer 1

1.The Ham Sandwich Theorem. 2.Fermat's Last Theorem (It wasn't his last. Fermat announced some results without proofs. This was the last one anyone else proved.)

Answer 2

There are lots, irrational numbers (literally "not ratio"), imaginary numbers, strange attractors, the hairy ball theorem, and so on.

Answer 3

I know maybe this is not an unexpected name in English, but here is one that made us giggle all the time: in group theory, there are a class of subgroups called "subnormal". In Spanish (and other romance languages), "subnormal" is a word used as an insult (back in the day it was the standard word for mentally disabled people, now it's very demeaning and it's plainly an insult, like the "R" word). So we studied group theory and one type of groups were always insulted.