In the context of Magic: The Gathering, LGS refers to a local game shop.
Local game shops sell Magic and other TCGs, and may for example also have miniatures, D&D and comics. They are the venue for the lower leves of Organized Play. Prereleases provide a casual play atmosphere and an enjoyable atmosphere to get a preview of new cards. Friday Night Magic (FNM) enables players to compete for special foil DCI cards and other prizes. These tournaments are mostly for amateurs and are a good place to start your Magic-playing career, but are only available at stores and clubs with Wizards of the Coast Premiere status. These are supported by Wizards Play Network