means A thin, fine, fleeting strand or trace of something — a bit of smoke, hair, cloud, or anything wispy and barely there.

from From Middle English 'wisp,' a small twist or bundle (think a handful of straw or hay), with likely Germanic kin — possibly related to words for 'wipe' or to the wispy idea of something twisted and light. It later drifted from a literal little bundle to anything thin and insubstantial, and lives on in 'will-o'-the-wisp,' the ghostly marsh-light that leads travellers astray — once imagined as a sprite named Will carrying a twist of burning straw.