A neologism referring to a sexuality where the mind is sexy, particularly if plumbing is unimportant. The sapiosexual has attraction to the mind instead of, or in place of, the body. Incisive, inquisitive, intelligent, thoughtful people are attractive instead. For sapiosexuality, a new concept can be foreplay.
It is important to note that this isn't the same as bisexuality; while many bisexuals proclaim that they are attracted to minds, others are attracted to different aspects of males and females, and still others are cyclical. Bisexuality isn't the enlightenment some think it is. In the original intent of the term, where a person's sex is unimportant,
A "wolfieboy" on LiveJournal claims to have coined the term back in the summer of 1998 (see http://www.livejournal.com/talkread.bml?journal=wolfieboy&itemid=2262),
though I think the meme itself has been around for longer than that. The combination of word roots used to form it is debatable (if I recall correctly, it translates as sexuality of knowing); sapiophilia was suggested as a better term, though that removes the hint that gender is unimportant to the given person.