Document specified to reference content when creating a website

I have my adress written in 30 html pages on my website. When I move I am going to want to change the address. Instead of going through the code and changing it for all pages, I am looking for a method to change it in one place.

What would be the best practice for this sort of problem? There will probably not be that many references that would need to be stored. Any help on the matter will be appreciated.