Tesla coil

from The Century Dictionary.

• noun a form of transformer for the production of oscillatory currents of high frequency and high voltage. See transformer.

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

• (Elec.) A transformer without iron, for high frequency alternating or oscillating currents; an oscillation transformer.

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

• noun A type of resonant transformer circuit used to produce high voltage, low current, high frequency alternating current electricity.

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

• noun a step-up transformer with an air core; used to produce high voltages at high frequencies