Staff on the game are essentially people who help run the game, help the players, run plots, run NPCs, etc. These are players with special privileges on the game who help facilitate the daily running of the game, answer questions and so on.
A staff team often has several ranks within their team, including 'staff' at the bottom of the ladder, 'admin' or 'royalty' in the middle, and 'wizards' at the top (sometimes with a headwizard overseeing it all). Each of these ranks generally have access to various levels of code and permissions which reflects the level of their responsibility on the game.