spark gap

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A gap in an otherwise complete electric circuit across which a discharge occurs at a prescribed voltage.

Century Dictionary and Cyclopedia

1. n. The open space between the terminals of the secondary circuit of an induction-coil, or the similar space in any electric circuit, across which the disruptive electric discharge in the form of spark takes place.

Wiktionary

1. n. A gap, between two electrical terminals, across which sparks are generated.
2. n. Such a gap as a component of an engine's ignition system, especially that between the electrodes of a spark plug.

GNU Webster's 1913

1. (Elec.) The space filled with air or other dielectric between high potential terminals (as of an electrostatic machine, induction coil, or condenser), through which the discharge passes; the air gap of a jump spark.

WordNet 3.0

1. n. the gap between two high-potential terminals
2. n. a component of an ignition system; consists of two shaped electrodes and the space between them