Two bits or half a nibble. Since a crumb encodes values from 0 to 
,
it can conveniently be represented using single quaternary
digit. However, the term "crumb" is rarely used in practice.
Crumb
See also
Bit, Byte, QuaternaryExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Crumb." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Crumb.html