WordNet (r) 3.0 (2006):

BLT
    n 1: sandwich filled with slices of bacon and tomato with
         lettuce [syn: bacon-lettuce-tomato sandwich, BLT]

V.E.R.A. -- Virtual Entity of Relevant Acronyms (February 2016):

BLT
       BLock Transfer


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

BLT
 /B?L?T/, /bl@t/, /belt/, n.,vt.

    Synonym for blit. This is the original form of blit and the ancestor of
    bitblt. It referred to any large bit-field copy or move operation (one
    resource-intensive memory-shuffling operation done on pre-paged versions of
    ITS, WAITS, and TOPS-10 was sardonically referred to as ?The Big BLT?). The
    jargon usage has outlasted the PDP-10 BLock Transfer instruction from
    which BLT derives; nowadays, the assembler mnemonic BLT almost always
    means ?Branch if Less Than zero?.


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

BLT

   1. /B-L-T/, /bl*t/ or (rarely) /belt/ Synonym for blit.
   This is the original form of blit and the ancestor of
   bitblt.  It refers to any large bit-field copy or move
   operation (one resource-intensive memory-shuffling operation
   done on pre-paged versions of ITS, WAITS and TOPS-10 was
   sardonically referred to as "The Big BLT").  The jargon usage
   has outlasted the PDP-10 BLock Transfer instruction from
   which BLT derives; nowadays, the assembly language
   mnemonic BLT almost always means "Branch if Less Than
   zero".

   2. bacon, lettuce and tomato (sandwich).

   [Jargon File]