You might have heard of or seen banjos with "scooped" fingerboards. A banjo with a scooped fingerboard is, usually starting after the 17th fret (the 18th - 22nd frets), the frets are not installed and the fingerboard is scooped down.
Why might someone want this feature? This is really only done on 5 string banjos that are meant for clawhammer playing. The closer to the bridge you play, the brighter the tone will be. As you move your picking hand further from the bridge, your banjo's tone becomes warmer and darker. Many clawhammer players prefer this darker tone and play above the fingerboard. By not having the frets in the way and the fingerboard being scooped down, it makes it easier for clawhammer players to play above the fingerboard.