Why is a fretboard binding?
Fretboard binding has the added bonus of preventing or at least hiding the edges of frets from sticking out and making fretting uncomfortable. Sometimes frets are poorly installed or more likely the fretboard wood shrinks slightly as it dries out which can make the frets stick out.
What are bound frets?
Binding is the practice of taking a strip of material—typically vinyl—to line the outside of the fretboard. That material decoratively covers the end of the frets that press into the wood (otherwise known as the “tangs”) at the edges of the fingerboard.