BLT /B-L-T/, /bl*t/ or (rarely) /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'.