Whenever you are trying to organise a large pool of digital content it’s not long before somebody uses the term metadata.
So what is metadata? If you look at a formal definition you will read something bordering on the existential like "data describing data".
I find the best way to start a conversation about metadata is to look at a familiar example like digital photography.
Lots of people have digital cameras and take loads of photos. These photos are typically stored as JPEG files that contain the actual photo and some information about the photo like: The date and time the photo was taken, where the photo was taken, the dimensions of the photo and the focal length used to take the photo.
This additional information is called metadata and in this case is captured automatically by the camera when a photos is taken.
Once you import your photos to a computer for use with photo management software like Windows Live Photo Gallery it can make use of the metadata captured against each photo in order to provide you with different views into your photo collection. For example you might want to see "photos taken on a specific day" or "photos taken in a specific location".
Managing a large collection becomes a lot easier when you are able to sort, filter and group your photos in this way but what if you wanted to see all the photos in your collection that has a boat in it?
Since your camera can’t determine (at least not yet) whether a photo contains a boat, you need to manually point out which photos do contain a boat. Capturing metadata manually is often refered to as "tagging".
The biggest benefit from the effort of capturing this information is that it allows you to get more specific views into your collection for example "photos of boats taken during my vacation to South Africa in March".