Ohio State runs a seminar called "[What is...?][1]" that I think meets your criteria.

From the webpage 

> The seminar's main goal is to expose culturally ambitious participants
> to some mathematical notions not taught in standard courses.  These
> topics form an important part of mathematical folklore, and may prove
> useful for doing research and enhancing teaching.
> 
> Lectures will be given mostly by graduate and undergraduate student
> participants.


  [1]: https://math.osu.edu/activities/colloquium/what-is