Patent drawing - TeslaBifilar - . Public domain image

Bifilar coil in Nikola Tesla's United States patent 512,340 of 1894. Tesla explains that in some applications (which he does not specify) the self-inductance of a conventional coil is undesired and has to be neutralised by adding external capacitors. The bifilar coil in this configuration has increased self-capacitance, thereby saving the cost of the capacitors. It is notable that this is not the kind of bifilar winding used in non-inductive wirewound resistors where the windings are wired anti-series to null out self-inductance.

It's also interesting to note that Tesla's bifilar coil is used in John Bedini's permanent back emf motor which are (alleged) overunity motors with open loop circuts. For more information see John Bedini.