Hysteresis is a term used in control systems and other places.
You've seen it on your household thermostat. The basic idea is that the point where the heat comes on is lower than the point where it turns off.
So the heat comes on when it's 17 degrees, but does not turn off until it is 19 degrees, so there is a band where it won't be turning on and off alla time.
In code its very simple, viz:
if (temp < coldPoint) turnOnTheHeat();
if (temp > hotPoint) turnOffTheHeat();
Nothing more to it.
a7