Also known as a toggle switch or a toggle.
The Switch component (toggle) is a digital on/off switch. Toggle switches are best used for changing the state of system functionalities and preferences. "Toggles may replace two radio buttons or a single checkbox to allow users to choose between two opposing states." - Source
May may also check out the Checkbox component.
How it should work
"Toggle switches should take immediate effect and should not require the user to click Save or Submit to apply the new state. As always, we should strive to match the system to the real world." - Source
When not to use it
Don't use it if the user is required to click save or update to apply the new state.
"The toggle labels should describe what the control will do when the switch is on; they should not be neutral or ambiguous. When in doubt, say the label aloud and append “on/off” to the end. If it doesn’t make sense, then rewrite the label" - Source
The label should describe what the toggle will do when the switch is on.