WordNet (r) 3.0 (2006):

fall through
    v 1: fail utterly; collapse; "The project foundered" [syn: fall
         through, fall flat, founder, flop]

The Free On-line Dictionary of Computing (19 January 2023):

fall through
fall thru

    (The American misspelling "fall thru" is
   also common)

   1. To exit a loop by exhaustion, i.e. by having fulfilled its
   exit condition rather than via a break or exception condition
   that exits from the middle of it.  This usage appears to be
   *really* old, dating from the 1940s and 1950s.

   2. To fail a test that would have passed control to a
   subroutine or some other distant portion of code.

   3. In C, "fall-through" occurs when the flow of execution in a
   switch statement reaches a "case" label other than by
   jumping there from the switch header, passing a point where
   one would normally expect to find a "break".  A trivial
   example:

    switch (colour)
    
    case GREEN:
      do_green();
      break;
    case PINK:
      do_pink();
      /* FALL THROUGH */
    case RED:
      do_red();
      break;
    default:
      do_blue();
      break;
    

   The effect of the above code is to "do_green()" when colour is
   "GREEN", "do_red()" when colour is "RED", "do_blue()" on any
   other colour other than "PINK", and (and this is the important
   part) "do_pink()" __and then__ "do_red()" when colour is "PINK".
   Fall-through is considered harmful by some, though there are
   contexts (such as the coding of state machines) in which it is
   natural; it is generally considered good practice to include a
   comment highlighting the fall-through where one would normally
   expect a break.  See also Duff's Device.


The Jargon File (version 4.4.7, 29 Dec 2003):

fall through
 v.

    (n. fallthrough, var.: fall-through)

    1. To exit a loop by exhaustion, i.e., by having fulfilled its exit
    condition rather than via a break or exception condition that exits from
    the middle of it. This usage appears to be really old, dating from the
    1940s and 1950s.

    2. To fail a test that would have passed control to a subroutine or some
    other distant portion of code.

    3. In C, ‘fall-through’ occurs when the flow of execution in a switch
    statement reaches a case label other than by jumping there from the switch
    header, passing a point where one would normally expect to find a break. A
    trivial example:


    switch (color)
    
    case GREEN:
       do_green();
       break;
    case PINK:
       do_pink();
       /* FALL THROUGH */
    case RED:
       do_red();
       break;
    default:
       do_blue();
       break;
    

    The variant spelling /* FALL THRU */ is also common.

    The effect of the above code is to do_green() when color is GREEN, do_red()
    when color is RED, do_blue() on any other color other than PINK, and (and
    this is the important part) do_pink() and then do_red() when color is PINK.
    Fall-through is considered harmful by some, though there are contexts
    (such as the coding of state machines) in which it is natural; it is
    generally considered good practice to include a comment highlighting the
    fall-through where one would normally expect a break. See also Duff's
    device.