What is a snippet?
For example, you could create a snippet that contains your company's copyright information. Wherever you want the copyright to appear, instead of typing it out again and again, you would use the snippet's merge code in it's place.
When the page displays, the snippet merge code is replaced with the snippet's content. When you need to update your copyright information, you can simply edit and update the snippet content, and the changes will be automatically reflected wherever the snippet was used.