This is a required field for the BGM category as I fill out the event information. But I am not hosting games that are part of a game system, just standalone boards that are not part of any series or franchise. 

For now I just put the game's name in there again, I think I can change it later. Is that ok? What should I be doing with this field?

The game system would be the name of the game.  Ie a game of settlers of Catan you could give a cute name for the event  “settlers come on” but the system would be the settlers of Catan.

Every game has a system.

For almost all board games, the name of the game is it's system.

As a side note: do not repeat information across multiple fields unless absolutely necessary. That means you should never have the game name/system in the description and it's often a good idea to have a title that is more than just the game name, as well.

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Derek Guder
Event Manager
Gen Con LLC