Post Closed as "no longer relevant" by Kevin Lin, quid, Qiaochu Yuan, Zev Chonoles, Gjergji Zaimi
2 added 42 characters in body

It's a common observation in Lie theory that Cartan matrices and the Killing form are named after the wrong people; they were discovered by Killing and Cartan, respectively. I remember learning about many other examples of this phenomenon, but can't think of too many at the moment. Wikipedia has a short listsome examples here and here, but I'm curious about more obscure examples. So I thought I'd ask MO for a nice list.

Bonus points for an interesting story behind why the concept was incorrectly named. Concepts that were deliberately named in honor of another mathematician don't count.