silver wedding 
(also silver wedding anniversary)
noun
The twenty-fifth anniversary of a couple’s wedding: they will be celebrating their silver wedding at a top London restaurant...
- The play is set in three time zones - the wedding night, the silver wedding anniversary, and then a further 23 years (the present day) later.
- The couple have three children and two grandchildren and have been on one cruise before, around the Caribbean aboard the Cunard Countess, to celebrate their silver wedding anniversary.
- They celebrated their silver wedding anniversary in March and have two children, Rebecca, 17, and Rachel, 19.