Tenses indicate the time and state of an action or event in relation to the time of speaking. There are three main tenses - present, past, and future - which can be further specified by mood, aspect, and other categories such as definite or indefinite, completed or not completed. Common aspects include the continuous and perfect forms. For example, the present continuous tense ("is playing") indicates a current ongoing action, while the past perfect tense ("had played") emphasizes that one past action was completed before another past action.