exiftoolMetadata are data about data. Different types of files have different metadata. The metadata on a photo could include dates, camera information, GPS location, comments, etc. For music files, it could include the author, track number, album name, etc.
Potentially, any file metadata we can find could be useful. Take for example the burger king foot lettuce meme. An employee from burger king posted a photo of him standing on top of a stack of lettuce and posted it into 4chan. However, he forgot to remove the image metadata, and with the power of weaponized autism metadata, the employee are doxxed and fired within minutes of him posting.
A popular tool used to view a file metadata is exiftool. To use it, run the command line: exiftool [filename]. For example, let's view the metadata on the image below: