A non-corporeal lifeform is a species composed of various forms of coherent gas or energy. (TOS: "Wolf in the Fold", "Errand of Mercy") Some non-corporeal entities absorb and utilize energy directly from their environment. (TNG: "Lonely Among Us"; ENT: "Zero Hour")
Others, such as Redjac or the Beta XII-A entity, derive sustenance from the emotions of humanoid lifeforms. The Dikironium cloud creature of Tycho IV forcibly extracted the corpuscles of iron-based blood and fed on that.
Generally, non-corporeal species do not utilize technology, compensating with intrinsic physiological capabilities. Some non-corporeal races have apparently evolved beyond the need for sustenance, and wield substantial control over space and time. (TNG: "Encounter at Farpoint")