The bontil is the place on the bottom of the glass where the blowpipe was attached. Pilgrim normally smoothed the pontil area. Some other glass manufacturers left it rough from when the cracked off the blowpipe.
Pilgrim Glass Arched Label
This was the label used on their newest products.
Note: the white areas are caused by reflections because this picture was taken outside in the bright sunshine. The actual vase is the rich cranberry color all over.