Generally speaking, an artist is a person that produces or practices any kind of art like paintings, sculptures or music. When it comes to metadata, the Artist information is usually displayed in audio files. They give information about the single artist or band that performed, but not necessarily, wrote the song or created the piece of recording.
The Artist can also be found in certain image files. More precisely, in photos that are either in their raw form (CR2, NEF, ARW, etc.) or already edited and saved for sharing and publishing (JPG, PNG, etc.). Here, the Artist refers to the photographer that took the photo.