[from the obvious mainstream scatologism]
n. 1. An awkward feature or programming technique that ought to be made cleaner. Using small integers to represent error codes without the program interpreting them to the user (as in, for example, UNIX 'make(1)', which returns code 139 for a process that dies due to segfault).
2. A technique that works acceptably, but which is quite prone to failure if disturbed in the least, for example depending on the machine opcodes having particular bit patterns so that you can use instructions as data words too; a tightly woven, almost completely unmodifiable structure.
Also in the adjectives 'crockish' and 'crocky', and the nouns 'crockishness' and 'crockitude'.