unknownbutton
nounUK /ʌnˈnəʊn ˈbʌtən/
US /ʌnˈnoʊn ˈbʌtən/
A button that you do not know what it does.
I pressed the unknown button and the screen went black.
OTHER MEANINGS
2. A key on a device that has no label or symbol.
The remote had an unknown button near the power switch.
3. A clickable spot on a screen that does nothing clear.
She tapped the unknown button, but nothing happened.
4. Something whose purpose is a secret or a surprise.
The game hid an unknown button that opened a bonus level.