"Terminus" is where you are heading to. If for example you are sitting at Freudstr. and you are going to drive the route to Stadtgrenze, then Stadtgrenze is your terminus. Therefore you need to put "Stadtgrenze" on your destination display

If you don't understand the IBIS system, you can just press "Alt" to bring up the menu then click the button with a route number symbol on it (something like | |9|2| on it). In this example, type in 92 in the first box and select "Stadtgrenze" from the list in the next box. Note that the passengers do not "look" at the route number - they just look at the destination. You could put up 587 Stadtgrenze and the passengers would still get on.