I saw a nice definition of tags on the del.icio.us home page today (which isn’t something I normally visit because of WebnoteHappy.) The definition goes like this:

Tags

A tag is simply a word you use to describe a bookmark. Unlike folders, you make up tags when you need them and you can use as many as you like. The result is a better way to organize your bookmarks and a great way to discover interesting things on the Web.

Very well put!