Simple explanation for an intimidating word. Maybe we should go with that. I'm glad you are no longer confused so let us go on and study spurs. Look at the map again. See if you can find contours 'going out' of the hillside.
Spurs are more evident around a hill or mountain, rather than on a long hillside.
But like reentrants, they too can be any size, anywhere, as long as the land falls away on three sides. But we will stick to spurs and reentrants for now and find how to tell which is which on the map while you are tired, bruised and far from home and the mosquitoes are biting. On a USGS topographic map the contours are labeled with their elevation. You can see the number 4000 then 4100 and it is obvious which way is up. Search for a hilltop.