1. hexadecimal.
2. A 6-pack of anything (compare quad). Neither usage has anything to do with magic or black art, though the pun is appreciated and occasionally used by hackers. True story: As a joke, some hackers once offered some surplus ICs for sale to be worn as protective amulets against hostile magic. The chips were, of course, hex inverters.
3. <character> The hash character, used to introduce hexadecimal constants in some assembly languages.
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