What does it mean watcher on eBay?

When buyers find items they are interested in they often click the "watch this item" button.

This basically bookmarks the item so that buyers can check on it at a later time.

They are not necessarily bidders of any kind; a watcher simply will watch an item for many different reasons and none of them may to be for your benefit. Sometimes, however, a watcher will watch and then bid as the auction comes to the end. A watcher should not affect anything you do on eBay.