Metadata is simply data about data. This can actually be a loop – like a mirror in a mirror – of data about data about data. In practical terms it’s data that describes properties about other data you have. Depending on the context something can be metadata or actual data. The main concept is that sometimes the information about your data is as important as the data itself.
One of the easiest ways to explain metadata is with digital photos. I’ve recently begun using Adobe’s Lightroom to better manage my extensive digital photo collection. Every time a digital photo is created there is metadata data created along with it. There is a standard known as EXIF – but if you look at the screen shot on the left you can see some information about this train photo I took some time ago. Some information is basic file information – such as the date and time or dimensions of the photo. However it captured a lot of detailed information – down to which lens was used on the camera. Lightroom can actually use this to make intelligent corrections to the image itself. Lightroom itself is based on managing data (the images) using metadata – in order to organize and enhance them.