Cite
 
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”.