The Collaborative International Dictionary of English v.0.48:

Nan \Nan\, interj. [For anan.]
   Anan. [Prov. Eng.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

nan
    n 1: your grandmother
    2: the mother of your father or mother [syn: grandma,
       grandmother, granny, grannie, gran, nan, nanna]
    3: a river of western Thailand flowing southward to join the
       Ping River to form the Chao Phraya [syn: Nan, Nan River]
    4: leavened bread baked in a clay oven in India; usually shaped
       like a teardrop [syn: nan, naan]

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

Not-a-Number
NaN

    (NaN) An IEEE floating point representation
   for the result of a numerical operation which cannot return a
   valid number value.  A NaN can result from multiplying an
   infinity by a zero, or from subtracting one infinity from
   another [what else?].

   NaN is encoded as a special bit pattern [what pattern?]
   which would otherwise represent a floating-point number.  It
   is used to signal error returns where other mechanisms are not
   convenient, e.g. a hardware floating-point unit and to allow
   errors to propagate through a calculation.

   Similar bit patterns represent positive and negative
   overflow and underflow and the positive and negative
   infinities resulting from division by zero.

   Bit patterns
   (http://psc.edu/general/software/packages/ieee/ieee.html).

   [ANSI/IEEE Std 754-1985].

   [Correct?]

   (2001-04-01)