Grabbing means that the mouse is confined to the application window, and nearly all keyboard input is passed directly to the application, and not interpreted by a window manager, if any.
When mode is SDL_GRAB_QUERY the grab mode is not changed, but the current grab mode is returned.
typedef enum {
SDL_GRAB_QUERY,
SDL_GRAB_OFF,
SDL_GRAB_ON
} SDL_GrabMode;