noun

• (informal) A regular.
  "I've been going to that chat room for months, and I know most of the regs by now."
• (informal) A regulation.
  "It makes me sad to see a prisoner complain about another prisoner not writing. His or her mailroom (or yours!) might have just tossed the letter; besides the rules and regs for prisoners writing each other are different in every state, and may change for no reason. Or, the rules may be ignored (especially for gay prisoners) also, even prisons that do accept mail from other prisoners, may not deliver it to people in isolation or on certain security levels."
• registration
  "What's your reg and where are you parked?"

noun

• (geography) A hard surface of rock fragments set in a sandy matrix, found in some hot deserts; regolith, stony desert.
  "As I say for half a mile round the fort it is rutted gravel. We call this sort of gravelly stuff reg."