Hysteresis describes how something appears or responds based on its history.
What we see in the present is that way only because of what happened in the past. Stretch a rubber band and upon its release, the band does not return to its original shape. That's hysteresis.
Understanding hysteresis means we can put its somewhat predictable behavior to good use. Take for example your smartphone's reaction to finger flicks.
Because hysteresis can be a dynamic lag between an input and an output that disappears if the input is varied more slowly—called rate-dependent hysteresis—a slow flick of your finger on the smartphone's screen inches up a list while a quick flick sends the list zooming forward.
We build the same rate-dependent hysteresis in PS Audio's volume control knobs. A slow turn inches forward the volume but a fast turn sends the level up or down quickly. This programming is not by accident.
As long as we're still in the audio category there's also something called hysteresis distortion. This kind of distortion occurs in audio products based on magnetic principles: loudspeaker drivers, crossover inductors, or all those magnetic components in a Class D amplifier. Once the passage of a varying audio signal magnetizes a piece of magnetic material in one direction, it retains that state. When our constantly changing audio signal then reverses direction, the magnet's historic memory adds or subtracts from the audio signal causing distortion.
Its history affects its future outcome.
It's not worth getting hysterical about hysteresis (I couldn't resist those words) but maybe fun to read up on it and how it affects our everyday life.
