/härt-ˌbēt/
n. 1. The signal emitted by a Level 2 Ethernet transceiver at the end of every packet to show that the collision-detection circuit is still connected.
2. A periodic synchronization signal used by software or hardware, such as a bus clock or a periodic interrupt.
3. The natural oscillation frequency of a computer's clock crystal, before frequency division down to the machine's clock rate.