∎

See also: ■ [U+25A0 BLACK SQUARE], and ⏹ [U+23F9 BLACK SQUARE FOR STOP]

Translingual

Etymology

Introduced into mathematical usage by Paul Halmos, modeled after the end sign ■ (a printer’s ornament or dingbat used to indicate the end of an article or story) found in popular print media.

Symbol

∎

1. (mathematics) QED.

Usage notes

The symbol itself is called a tombstone or halmos in English.