A pontil or punty (also called a pontil rod or punty rod) is a long solid iron rod used principally for gathering molten metal (glass in its liquid or molten or fused state ready for processing) for the pressing mold.  It is also used for holding an article or pressed glass after pressing for supplementary or finishing operations while the glass is still hot enough for forming.
      A Pontil Mark is a rough mark in the center of the bottom of a glass object where the pontil was attached (See A below) In common usage referred to in abbreviated form as the 'pontil' in spite of the fact that the word alone refers to the tool and not the mark it leaves.
      This scar is frequently ground and polished to a smooth circular concave impression (see B below) & remains as evidence of the pontil rod having been used.  It is important to know that this pontil mark can also be found occasionally on pressed glass, mainly on very early EAPG, although it generally is on blown ware.

A:  These are rough pontils. The pontil on the left is from a molded tumbler & the pontil on the right is from a blown decanter.

B:  A ground pontil.  The arrows point to the circumference of the circle showing the area that was ground on the foot of this goblet.
    C:  No pontil

Reference: Pressed Glass in America
by John & Elizabeth Welker