Learn something every day. I thought it referred only to sound or vision. stereo- a combining form borrowed from Greek, where it meant “solid”, used with reference to hardness, solidity, three-dimensionality in the formation of compound words: stereochemistry; stereogram; stereoscope.
Yes, this is a glitch that was never resolved in spite of the reports we made. I've removed it from the course. Thanks for the screenshot. Warning it may take a few days before this sentence is no longer used so if you get it again don't be surprised...or just leave out the space and go on.