Like some moving parts of other machines, some switches do have “overtravel”. What exactly is over-travel for a switch? In general, it is the distance a button/actuator can be pressed beyond the operating distance without damaging the mechanism. Typically, this terminology applies to limit switches/micro-switches. Here is a good visual to show what this may look like when you actually press a switch.
If a button forcefully gets pushed further beyond the over-travel height, it will likely break the mechanism. Datasheets usually combine these dimensions on one drawing without showing a change in height for convenience.