There are many controversies on energy—time uncertainty relation. Because of the confused role time plays in quantum mechanics, the references and meanings of energy—time uncertainty relation are different in different explanatory contexts. But what do time and energy really mean? What is the philosophical foundation of this relationship? The article bases on the three different meanings of time in quantum mechanics, discusses the references and meanings of energy—time uncertainty relation in various contexts, and aims to clarify the confusion on the references and the meanings of the uncertainty relation between energy and time.