Fall
Fall or Falloff or Spill is a downward drop from a specific note to an indefinite ending pitch.
Brass players glide down through the overtone series, smoothing the shape using half valves on trumpet or the slide on trombone.
Saxophone and woodwind players lightly finger a descending chromatic scale.
Falls may be short or long as indicated by the length of the curved line off the note.
References
"Arranging for Large Jazz Ensemble" by Dick Lowell and Ken Pullig, Berklee Press, Boston, 2003, page 9