What is the X in X-mas?
A bacon, lettuce, and tomato sandwich: the Lodge where MTV V.J.'s get B.L.T.'s A.S.A.P. (1950s+)
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).