noun
coil; coiled shape
Refers to something coiled up, especially a snake or a rope. Often used in the phrase とぐろを巻く (to coil up).
ヘビがとぐろを巻いている。
The snake is coiled up.
ロープがとぐろを巻いて床に置いてあった。
The rope was lying on the floor in a coil.
渦巻き refers to a spiral or whirlpool shape, often dynamic or fluid, while とぐろ specifically describes a static, layered coil like a snake or rope.
The origin is uncertain. It may be related to the verb とぐる (to coil), but the exact derivation is unclear.