Interviewed by some startups (Berlin) I have been asked if I know or to explain them what they are doing... and the funniest thing is they were serious.
Most companies should have that explained on their website - If you haven't done enough diligence to repeat what's on the website, you may not be a good candidate.
And that’s a valid answer. “I went over your web site and read some press releases but I’m not quite sure what you do yet. I think it is along these lines...can you explain further?”