All mechanical contacts, when actuated, tend to open and close one or more times after the contact is closed.
This process is called bouncing
(from rebound). The consequences of bouncing can be avoided by electronic components. The problem of bouncing has only become virulent with
the advent of modern digital and microcomputer technology, since the high processing speed means that all input signals, including interfering signals such as bounce, are evaluated accordingly by the subsequent circuitry.
Debouncing can be avoided with RC gates and downstream flip-flops.