The Jargon File (version 4.4.7, 29 Dec 2003):

trit
 /trit/, n.

    [by analogy with bit] One base-3 digit; the amount of information conveyed
    by a selection among one of three equally likely outcomes (see also bit).
    Trits arise, for example, in the context of a flag that should actually
    be able to assume three values ? such as yes, no, or unknown. Trits are
    sometimes jokingly called 3-state bits. A trit may be semi-seriously
    referred to as a bit and a half, although it is linearly equivalent to
    1.5849625 bits (that is, log_2$(3) bits).


The Free On-line Dictionary of Computing (30 December 2018):

trit

    /trit/ (By analogy with "bit") One base-3 digit; the
   amount of information conveyed by a selection among one of
   three equally likely outcomes.  Trits arise, for example, in
   the context of a flag that should actually be able to assume
   *three* values - such as yes, no, or unknown.  Trits are
   sometimes jokingly called "3-state bits".  A trit may be
   semi-seriously referred to as "a bit and a half", although it
   is linearly equivalent to 1.5849625 bits (that is, log2(3)
   bits).

   [Jargon File]

   (1995-05-11)