An annual calendar is a complication that tracks and displays the day, date and month on a timepiece. It automatically adjusts the date for months with 30 or 31 days but unlike the perpetual calendar complication it needs to be corrected once a year at the end of February.
Fun fact: it was actually the Patek Philippe manufacture that created the annual calendar complication recently in 1996. It had almost all the suave of the perpetual calendar complication but its need for a yearly correction meant that the movement within could be simplified thus making them more affordable to produce. That being said, it’s still a Patek Philippe, so ‘affordable’ is not really as affordable as you expect.