Global Priority Mail (GPM): A category of international mail that provides fast service at attractive rates to 27 countries.
Grill: A pattern of small, square pyramids in parallel rows impressed or embossed on the stamp to break paper fibers, allowing cancellation ink to soak in and preventing washing and reuse.
Gum: The coating of glue on the back of an unused stamp.
The narrow space between stamps in the sheet permitting perforation. [see Perforation]
The blank margins dividing a sheet of stamps into panes.