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1. (Or "hand cruft") To Translate a hot spot of a program in a HLL into assembly language by hand, as opposed to trying to coerce the compiler into generating better code. Both the term and the practice are becoming uncommon.
See tune, bum.
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.