black <#stamp=stamps> issued in 1923 to mourn the death of President Warren Harding; <#scott=Scott> 610-613.

series of <#commem=commemorative>  <#poststamp=postage stamps> honoring Black Americans; begun in 1978 with the Harriet Tubman stamp (<#scott=Scott> 1744).

nickname for the black 2¢ Andrew Jackson <#stamp=stamps> and <#postenv=postal envelopes> first issued in 1863.  Examples: <#scott=Scott> 73 and U46.

an impression made by <#perf=perforating> pins in a place where perforations were intended, but from which <#chad=chads> were not removed.  These interesting varieties are not <#imperf=imperforate> stamps.  Blind perforations are considered <#freak=freaks>, not <#error=errors>.

a unit of <#stamp=stamps>, generally four or more in number.