What are the main differences between a tankless water heater and a tank water heater, and which one is more efficient for providing hot water in a household?

A tankless water heater heats water on demand, while a tank water heater stores and heats a large amount of water continuously. Tankless heaters are more efficient because they only heat water when needed, while tank heaters can waste energy keeping water hot. Tankless heaters are generally more efficient for providing hot water in a household.