What is the D in a white circle on the gear selector indicator on 1992 Ford Ranger? It is followed by D 1 2 3?

What is the D in a white circle on the gear selector indicator on 1992 Ford Ranger? It is followed by D 1 2 3?

The circled "D" is the normal driving position. The other positions are to leep the transmission in the selected gear for specific purposes such as towing or when road conditions require more control as in climbing or decending hills when the truck is carrying a heavier load.