(from German/Yiddish: "air person", "human being in the air" - plural, where it exists, is Luftmenschen). The opposite of a materialist, may be the opposite of an achiever too. Someone whose strengths and pursuits are non-practical (may indeed be helplessly handless), not related to any sort of business or worldly gain. May be a shlemihl, may be a useless sort of geek. Is very likely to have an interest in things of the intellect and/or the spirit, art, music and philosophy. May at best be a source of knowledge and wisdom for others, even if an exasperation to those closest to him/her, and indeed himself/herself. For sociological reasons, usually male.
If your head is often in the clouds, and you don't even think you can live on air, you are probably a Luftmensch.
A Luftmensch is a good friend for holistic, unbiased and unpushy advice, and useless as a breadwinner.