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In plumbing, a sink is a bowl-shaped device, usually made of porcelain, that is used for washing hands or small objects such as nylons, socks or underwear. When a sink becomes stopped-up or clogged, a person will often resort to use of chemical drain cleaner or a plunger.
In electromagnetic theory sink and source are respectively the termination or supply of current flow; the divergence of the current density is their negative and positive, respectively.

More generally this idea can be applied to vector fields other than current density; for example, mass is a sink of gravitational field strength.

A TTL (Transistor Transistor Logic) circuit will "sink" current when the circuit is a logic "0" (grd) and "source" current at a logic "1" (+5vdc).

[These terms are far more generally used than just in digital electronics. Indeed, they antedate digital electronics. They are used in thermodynamics, which originated in the 19th century, and also for other physical systems such as rivers. Would some physicist complete this article?]