A coil is a series of loops. A coil made of rigid materials can be fashioned in a spiral or helical shape; see spiral staircase. Flexible materials like wire, rope, hose, or cable can also be coiled into empty loops, or wound around a central drum or spindle.

In electrical engineering, an induction coil is formed when a metal wire is coiled around a core to create an electronic inductor. Polyphase coils are coil systems with multiple phases.

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