spark gap

from The American Heritage® Dictionary of the English Language, 5th Edition.

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

from The Century Dictionary.

• noun 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 a spark takes place.

from the GNU version of the Collaborative International Dictionary of English.

• (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.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the gap between two high-potential terminals
• noun a component of an ignition system; consists of two shaped electrodes and the space between them