Galleon - Gold coloured wizarding currency. Approximately £4.97 GBP or $10.17 USD. There are 493 Knuts to a Galleon and 17 Sickles to a Galleon. 

Gamp's Laws of Elemental Transfiguration - The fundamental principles for performing transfiguration. They are the primary exceptions which human beings cannot conjure and must strive for and earn for themselves: food, money, life, knowledge and love.

Ghosts - The spirit of a deceased wizard or witch. They were either afraid of death or have an extremely strong connection to the location they haunt and have left an imprint of themselves. They are a grey-silver colour, are weightless and can fly. They are able to pass through solid objects but create disturbances in water, fire and air. They cannot be destroyed but can be petrified if they look at a Basilisk. Once one becomes a ghost they are unable to move beyond the veil, and so will stay a ghost until the end of time.

Goblins - Highly intelligent creatures who run the Gringotts bank and are brilliant metal-smiths. They have long fingers and feet and speak the language Gobbledegook.

Gringotts - The bank for the wizarding world located in Diagon Alley. Ran by Goblins with vaults heavily guarded by enchantments and dragons. Vaults require a key and you are taken to your vault by a Goblin in a cart.

Gryffindor - One of the houses at Hogwarts, founded by Godric Gryffindor. Students traditionally show such traits as courage, chivalry and determination. The emblem is a lion, the house colours are red and gold, and the house ghost is Sir Nicholas de Mimsy-Porpington AKA Nearly Headless Nick.