[KyJim]

Right, "metadata" generically means information about a file or data about other data. So, metadata about phone calls would be the numbers called from and to, the dates and times, length of calls, and even location of the parties during the conversation (via cell tower). That can be pretty powerful information by itself. Metadata about emails would include sender, recipient, subject line, length of message, when sent, when received and when read, and how the message was routed (locations, etc.).

When you take a photo with a digital camera or smart phone, there is normally metadata imbedded in the photo itself which will vary by device. It can include location information (GPS enabled smart phone), dates, shutter speeds (on some cameras), and other information. The metadata which websites may glean from your visits include your email address (depending upon browser settings), browser used, and your URL. They can also use tracking cookies to see other places you visit. A lot of sites use advertising which employs tracking cookies to see where you visit so they can target ads to you. All this is metadata.

The metadata about the website itself, or the webpage, often includes what html editor or other programs were used to create the page or website, version of html used, descriptive information that they hope search engines will pick up, and other information not displayed on the page itself in a browser. I doubt this is very useful to intelligence agencies on a widespread basis.