Black hole

A place of punitive confinement; a lockup or cell; a military guardroom.

A gravitationally domineering celestial body with an event horizon from which even light cannot escape; the most dense material in the universe, condensed into a singularity, usually formed by a collapsing massive star.

A void into which things disappear, or from which nothing emerges; an impenetrable area or subject; an area impervious to communication.

A place where incoming traffic is silently discarded.

"One way of fighting spam is to use a blackhole list maintained on a blackhole server."

To redirect (network traffic, etc.) nowhere; to discard (incoming traffic).