A content inventory is a list of all the content on your site.If you are revising a Web site, start with a content inventory of what is now on the site. Then, use your Web site requirements to create a planned content inventory for the new version of the site.

If you are developing a new site, of course, you will only have the planned content inventory.
In any situation, you have to know what you are working with. The content (the information) is what your site offers to your users. You have to know what you are now offering and decide whether each piece of it is still needed; still accurate; and still written in the right level of detail, the right tone, and the right language for your users.

Many Web sites grow by accretion. People keep adding pages to the Web site, but few pages ever get taken away. After a while, if you don’t keep a content inventory, no one knows what is on the site. It could have outdated and inaccurate information. It could have pages that contradict each other. It is very hard to maintain a site if you don’t have a content inventory.

If you are developing a new site, setting up a content inventory at the beginning puts you on a good path. If you keep up the inventory as the site matures, you will continue to know what is on the site, how old each page is, when each page has been revised or needs to be reviewed, and so on. For more news: usability.gov/design/inventory.html