I take that to mean cash in the sense of liquid assets, as opposed to something leveraged or what have you. Not cash in the sense of a briefcase full of cash.
Usually it means either cash or a cashier's check. Sometimes wire-transfer is also accepted. For lower-value items (police auctions of bikes and the like) people normally pay actual cash. For higher-value items (e.g. home foreclosure sales), people more often bring a cashier's check or wire the amount (depends on the jurisdiction).
