1. (Perhaps by analogy to a bouncing check) An electronic mail message that is undeliverable and returns an error notification (a "bounce message") to the sender is said to "bounce".
2. To play volleyball. The now-demolished D. C. Power Lab building used by the Stanford AI Lab in the 1970s had a volleyball court on the front lawn. From 5 PM to 7 PM was the scheduled maintenance time for the computer, so every afternoon at 5 would come over the intercom the cry: "Now hear this: bounce, bounce!", followed by Brian McCune loudly bouncing a volleyball on the floor outside the offices of known volleyballers.
3. To engage in sexual intercourse; probably from the expression "bouncing the mattress", but influenced by Roo's psychosexually loaded "Try bouncing me, Tigger!" from the "Winnie-the-Pooh" books.
4. To casually reboot a system in order to clear up a transient problem. Reported primarily among VMS users.
5. (VM/CMS programmers) Automatic warm-start of a computer after an error. "I logged on this morning and found it had bounced 7 times during the night"
6. (IBM) To power cycle a peripheral in order to reset it.