Or to the human mind, technically, but generally most people use it to mean finding smart sexy. A blend of sapient (from Latin sapiens, wise or sagacious) and sexual. The first citation found by WordSpy is a 2003 LiveJournal post from someone who claimed to have coined it in 1998. To quote from it:
I want an incisive, inquisitive, insightful, irreverent mind. I want someone for whom philosophical discussion is foreplay. I want someone who sometimes makes me go ouch due to their wit and evil sense of humor. I want someone that I can reach out and touch randomly ... I decided all that means that I am sapiosexual.