tapping

noun4

1. •
   An act of making a light hit or strike against something.

   • As he was speaking there was a soft tapping at the door. I went over and opened it […] — 1897
2. •
   A guitar technique in which the strings are tapped against the fingerboard
3. •
   The process by which a resource is tapped or exploited.

   • Competitive tappings of a common oil pool can lead only to waste and overproduction, unless rigidly regulated […] — 1938
4. •
   A connection made to some point between the end terminals of a transformer coil or other component.

   • The essential feature is that two adjacent transformer tappings are connected to the load simultaneously, each connection having a self-excited transductor in series; […]. — 1962