Teff is used for injera, a staple of Ethiopian cooking that is kind of a sourdough spongy flatbread. Teff can be mixed with wheat, but I've read it has an effect on gluten development unless it's been heat treated. (I think it encourages too much enzyme activity.)

I have some teff but didn't like anything I made with it, I haven't tried making injera, but I've had it at a restaurant in San Diego.