NOUN (2)

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;

The Collaborative International Dictionary of English v.0.48:

Spark gap \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.
   [Webster 1913 Suppl.]

WordNet (r) 3.0 (2006):

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