Bistability is a particular case of multistability, the property of a system to reside in different stable steady-states without being able to rest in intermediate states .
Properties of bistable systems
Often, bistable states are maintained by the help of positive feedback, negative feedback on the other sate players, self-catalysis.First decribed by Monod and Jacob in 1961 . Often found in combination.
Characteristic of the system to respond to stimulus in a non linear fashion, contribute to a "all or none" behavior. Ultrasensitivity can arise by multiple ways, including cooperativity. It account for the emergence of threshold levels of activation of a given transition.
History dependent behavior, kind of memory also here. An example of hysteresis is the liquid-to-gel transition of agarose- you need to heat it at around 90°C to liquefy it, but to maintain it at only 60°C to keep it liquid. In biology, key example include the lactose operon, or the activation of cdc2-cyclinB1. In both case the system requires less stimulus to maintain the state than for switching to this state. The refractory period in neuron stimulation is also a good example see here.