Global Priority Mail (GPM) : A category of international mail that provides fast service at attractive rates to 27 countries.

Graphite lines : A method of marking stamps for automatic sorting of mail. Used on some British stamps.

Greetings stamp : Stamp intended for use on birthday or other greetings mail.

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 to form an adhesive when wetted.

Gutter : The narrow space between stamps in the sheet permitting perforation.

Gutter margin : The blank margins dividing a sheet of stamps into panes.