Certain station lines, loops, sidings or bi-directional sections or similar can have multiple "berths". On a traditional panel, typically only one would be displayed to the signaller. The others being classed as hidden berths.
So for example, with a permissive freight only loop, if it was long enough, it may be that it would be specified that the TD must be capable of handling three descriptions. The first train entering the loop would have it's description shown. But the second and third trains entering behind the first train would have their descriptions stored in hidden berths. When the first train exited the loop, as the description stepped forward, the description of the second train would appear
For bi-directional sections, there would be two hidden berths, and depending on which direction was in use, the display berth would show the contents of one of these.
With the advent of VDUs, there is no extra cost for display berths, so now, mostly, there are less or no hidden berths, hence a section my have one, two or three display berths...
OpenTrainTimes displays them more like a signallers VDU. Traksy uses a different layout to save space on screen.