Trefor means “large village”. In PDL it is the junction between the lines to PD (right) and to Afon Wen (left).
In the model it serves as a way to form a continuous loop as the Afon Wen line goes to the storage siding with a bypass that goes back to PJL. Also in the picture on the top left is the single WR line falling steeply from Tan-Y-Graig towards Pwhelli. Obviously this is modeller’s license at work as this is miles away to the South on a map.