El Camino Bignum /el' k*-mee'noh big'nuhm/ n. The road mundanely called
   El Camino Real, running along San Francisco peninsula. It originally
   extended all the way down to Mexico City; many portions of the old road
   are still intact. Navigation on the San Francisco peninsula is usually
   done relative to El Camino Real, which defines {logical} north and south
   even though it isn't really north-south in many places. El Camino Real
   runs right past Stanford University and so is familiar to hackers.

   The Spanish word `real' (which has two syllables: /ray-ahl'/) means
   `royal'; El Camino Real is `the royal road'. In the FORTRAN language, a
   `real' quantity is a number typically precise to seven significant
   digits, and a `double precision' quantity is a larger floating-point
   number, precise to perhaps fourteen significant digits (other languages
   have similar `real' types).

   When a hacker from MIT visited Stanford in 1976, he remarked what a
   long road El Camino Real was. Making a pun on `real', he started calling
   it `El Camino Double Precision' -- but when the hacker was told that the
   road was hundreds of miles long, he renamed it `El Camino Bignum', and
   that name has stuck. (See {bignum}.)

   [GLS has since let slip that the unnamed hacker in this story was in
   fact himself --ESR]

   In recent years, the synonym `El Camino Virtual' has been reported as
   an alternate at IBM and Amdahl sites in the Valley. Mathematically
   literate hackers in the Valley have also been heard to refer to some
   major cross-street intersecting El Camino Real as "El Camino Imaginary".
   One popular theory is that the intersection is located near Moffett
   Field - where they keep all those complex planes.


Source: The Jargon File