Quick meaning
A customisable physical button on newer iPhones that can be set to perform a chosen function with one press.
Think of it like this
Like a programmable shortcut key on a remote control.
Where you may see this
You may hear this when buying a device, asking for repairs, or checking phone and computer settings.
Why it matters
Understanding the hardware term helps you choose the right device and explain problems more clearly when asking for help.
Say it simply
Action Button means: A customisable physical button on newer iPhones that can be set to perform a chosen function with one press.