What is metadata?
As a photographer, metadata is extremely useful. It allows me to embed my information into every photograph that I produce.
Simply put, metadata is "data about data". It is the information recorded inside of a file to give us more details about it. The time and date it was created, where it was created, the purpose of its creation, keywords, etcetera.
This is going to be an extremely quick explaination for those of you who just want to understand the bare bones and nothing more.
When dealing with photographs, there are three important "categories" within the metadata.
File Properties: This is the most basic of the three categories. Pretty self-explainatory. This is information about the actual file...when it was originally created, which folder on your computer, if it was modified, etc.
Camera Data (Exif): The exif data is information plugged into each image by your camera. It contains information about the camera, lens, flash, etcetera, used to capture the image. It also contains the exposure information for each image (your aperture value, shutter speed, and ISO) though it is not displayed in the above diagram.
IPTC Core: The IPTC Core is a lovely chunk of information applied through the computer (I have my full metadata template apply to each photograph that I import into Lightroom) which tells the viewer of the file whatever you want it to. You can fill in keywords, descriptions, and client names... but most important is probably the creator information. Ten years down the road, one of my files could end up on the desk of Life Magazine and they now have the contact information to find me and request usage permission! Although I am pretty sure it doesn't just happen like that ;).
I hope you've learned something today. This is just the absolute basics. You can learn much much more about metadata by doing a simple google search. But here are a few more links to get you started: