When the flight status, displayed in the arrivals hall, changes to "landed" or "arrived" - what exactly does it mean?

Let's say it says "Landed 21:53", does it mean:
a) the plane touched ground at 21:53
b) the plane reached the gate and began docking at 21:53
c) the passengers started leaving the plane at 21:53

Does anyone have experience from within the control room?