A summer shinding is a party, that is held in the episode Sun Bleached.
The party is held every year by Craig Mammalton. He gives invitations to people who are well tanned, but those that are not have to wait outside. Everyone who wants to go inside has to be checked by Craig to see if they are tanned and OK for the party.
The shinding is probably held near the Goo Lagoon. The door is made out of two huge stone figures, which have a shield in one hand. The statues are there as a decoration. Beside the door is a huge trash container, where all the un-tanned have to wait.