A choke is an inductor placed in a power supply line to isolate RF to some section of the circuit. It needs enough inductance to strongly attenuate the RF frequencies that would otherwise be spread to other parts of the circuit.
A choke most of the time is a coil with a low Q.
It is ment to smother signals that you don't want to spead to other parts of you circuit.
More information on coils can be found in the EDUCYPEDIA. http://www.educypedia.be/electronics/coilsrelay.htm