1.To pierce so as to let out, or draw off, a fluid; as, to tap a cask, a tree, a tumor, a keg of beer, etc.
2.Hence, to draw resources from (a reservoir) in any analogous way; as, to tap someone's knowledge of the Unix system; to tap the treasury.
3.To draw, or cause to flow, by piercing. "He has been tapping his liquors."
4.(Mech.) To form an internal screw in (anything) by means of a tool called a tap; as, to tap a nut, a pipe, or tubing.
5.To connect a listening device to (a telephone or telegraph line) secretly, for the purpose of hearing private conversations; also, to obtain or record (information) by tapping; a technique used by law enforcement agencies investigating suspected criminals. In the United States it is illegal without a court order permitting it.
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