An apology letter is a written expression of regret and responsibility for a mistake or wrongdoing. It aims to acknowledge the error, explain the context if necessary, and convey sincere remorse. The letter typically starts with a clear apology, explicitly stating what the writer is sorry for. It includes an acknowledgment of the impact on the recipient, demonstrating empathy and understanding. The writer takes responsibility without making excuses, offers a plan to rectify the situation or prevent recurrence, and ends with a commitment to making amends and a positive outlook for the future.