1. The practice of translating a hot spot of a program in a hll into hand-tuned assembly language, as opposed to trying to coerce the compiler into generating better code. Both the term and the practice are becoming uncommon.
See tune, bum, by hand; synonym with cruft.
2. More generally, manual construction or patching of data sets that would normally be generated by a translation utility and interpreted by another program, and aren't really designed to be read or modified by humans.