An anniversary clock is one of those glass domed clocks with the rotating pendulums that used to be so ubiquitous in old peoples homes when I was a kid. My parents have one from when they were first married.

It is called an anniversary clock because it only has to be wound once a year... thus, you can always wind it up on your anniversary. The new ones defeat the purpose because they are quartz movement and run on batteries... thus, retardedly, don't need to be wound...