Final answer:
Tam Lin is best described as a song/poem/story from the Scottish Borders, encompassing elements of mythology and folklore, and not strictly a character, historical event, or mythological figure.
Step-by-step explanation:
The character Tam Lin is often mistakenly categorized due to the various forms in which the story appears. However, Tam Lin is most accurately described as option d) Tam Lin is a song/poem/story. The ballad of Tam Lin, originating from the Scottish Borders, tells the tale of a young knight who is ensnared by the Queen of the Fairies and eventually rescued by his true love. In literary terms, Tam Lin is not a character from a novel, nor an event in history, nor purely a mythological figure, although the story does incorporate elements of mythology and folklore.