tbc stands for 'to be confirmed'. It goes next to a detail on a schedule, invitation, or plan that is probably right but not yet final: 'Kick-off 3pm (tbc)', 'Venue: Room 204, tbc'. The useful difference from TBA is the amount of information behind it. TBA means nothing has been announced yet — often nothing has been decided. TBC means there IS a plan, and someone just needs to make it official. So if a friend writes 'Saturday 7pm tbc', you can start making plans, but do not buy anything you cannot get a refund on. It is written English only, most common in British usage and in workplaces, and you will see it as TBC, tbc, or in brackets after the detail. It can also mean 'to be continued' at the end of a story or an episode, though most people write that out in full.