The gamemode library provides functions relating to the gamemode system in Garry's Mod. This entire library also passes through the C -> Lua bridge.
any gamemode.Call( string name, vararg args )
Called by the engine to call a hook within the loaded gamemode. The supplied event 'name' must be defined in the active gamemode. Otherwise, nothing will happen - not even hooks added with hook.Add will be called. This is similar to hook.Run and hook.Call, except the hook library will call hooks created with hook.Add even if there is no corresponding gamemode function.
table gamemode.Get( string name )
This is used internally - although you're able to use it you probably shouldn't. This returns the internally stored gamemode table.