What's convoluted about a convolution reverb?

It's a mathematical term. Don't know if this'll make it any clearer, but here's a broad definition: http://en.wikipedia.org/wiki/Convolution
 
Here's a less-general explanation of convolution as it applies to digital signal processing: http://www.dspguide.com/ch6.htm. There the author defines it as "a mathematical way of combining two signals to form a third signal". 
 
The word's common usage means to combine two things by coiling, folding, winding or twisting them together, or to describe something that's twisty, like the folds of a brain. It can mean something that's non-linear, meandering or difficult to follow, e.g. "convoluted logic". This isn't the definition we're using in the context of reverb, but rather the "combining" definition.
 
In the context of reverberation, you're combining your own signal with a signal recorded elsewhere, usually a burst of white noise in a real, physical space. In this way you emulate what your own instrument or voice would sound like in that space.
 
P.S. Here's a pretty good article on convolution reverbs: http://www.bhphotovideo.com/find/newsLetter/Convolution-Reverb.jsp/

As a word dork, I would like to say thanks to Bit.  I never really put "convolution" reverb together with "convoluted" as an adj.  Very cool!