A birthday calendar is a tool used to keep track of the birthdays of friends, family, and colleagues. It can be a physical calendar, a digital app, or a simple list. By noting these special dates, individuals can remember to celebrate and send greetings, ensuring that no important birthday is overlooked. Many people use birthday calendars to plan celebrations or buy gifts in advance. Some digital calendars even send reminders as the date approaches. This helps maintain relationships and shows appreciation for loved ones, making it a thoughtful way to acknowledge important milestones in their lives.