When the flight status changes to "landed" - what exactly does it mean?
 

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?

Really depends what resource you are using to get this response. But usually it means the plane has made the runway, and hasn't yet blocked into the gate.

as Craig6z stated, the general translation is:
on the ground = "LANDED"
at the gate, engines off, parking brake set = ARRIVED

for the geeks, from my long-ago Boeing Flight Test days, these corresponded to ACARS "ON" and "IN" respectively

Landed usually means landed. Whether that is the instant the wheels touched the runway or when the aircraft turned off the runway is a bit murky. But, also not generally important to other than ATC and air carrier ops types.

What is the specific reason for your question and perhaps someone here can provide you the underlying answer?

I'm just trying to make sense of the information displayed in the arrivals hall (and on the airport website) when I'm picking somebody up. I feel like it always takes way longer than expected for people to show up after the flight status gets set to "Landed" (I haven't really seen any airport that differentiates between "Landed" and "Arrived").

In one recent case, people started showing up about 30 minutes after the flight status was set to "Landed". My friend whom I was picking up claimed they actually touched ground "5-10 minutes ago".