Any one of the acalephs, esp. one of the larger species, having a jellylike appearance. See Medusa and acaleph.

Approximately 200 transparent or translucent marine species in the phylum Cnidaria and class Scyphozoa that spend a majority of their life in the medusa stage that follows an immature, polyp stage. Medusae have a central, radially symmetric bell (or “medusa”) and tentacles called nematocysts that hang below in order to stun and ensnare prey.

Some inflatables "jellyfish" rythmically when they fly in the air, hence the term. This is due to either poor design, or varying wind conditions, or the kite losing air and flopping around more than your manhood hanging free.

large siphonophore having a bladderlike float and stinging tentacles