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