What exactly is a runtime error?

It would be cool if using the search feature of this site answered this question. But, since it doesn't, I'll ask here.

 

I keep getting

 

A Runtime Error has occurred

Do you wish to debug?

 

Line 37

Error; Object expected

 

Clicking yes starts a "debugger" which pops a bunch of windows up on the screen that don't do anything. What is all this for?