To celebrate a significant anniversary, many couples wish to renew their Wedding Vows.
This can be formal or very informal, and is often done in Church or Chapel, performed by a Pastor or Priest, or perhaps in the local park, with the ceremony performed by a friend.
Couples who perhaps did not have a big White Wedding, wish to have that celebration now, and invite all their friends and family to the event, others, wish to quietly re-dedicate themselves to each other, with family and friends in attendance.