Debounce
Also called debounce time
Debounce is the short window after a press during which a keyboard or mouse ignores extra signals from the same switch. Metal contacts bounce for a few milliseconds when they meet and debounce stops that from counting as several presses.
As a switch wears its bounce gets longer. Once it outlasts the debounce window the device starts sending double presses, which is where chatter comes from.
In practice
Every mechanical switch bounces for a few milliseconds as its contacts meet. Firmware hides that by ignoring changes during a short debounce window after each press. Gaming keyboards and mice sometimes shorten the window to cut delay, which leaves less margin for a worn switch. When the bounce outlasts the window, the device reports it as a second press.
How to check
You can’t see the debounce setting from a browser but you can see what gets past it. The mouse test flags clicks less than 50ms apart and the keyboard test counts presses per key. If doubles appear, check whether the device software has a debounce option and try a longer value. If doubles continue, the switch itself is worn.