The Collaborative International Dictionary of English v.0.48:

Shad \Shad\ (sh[a^]d), n. sing. & pl. [AS. sceadda a kind of
   fish, akin to Prov. G. schade; cf. Ir. & Gael. sgadan a
   herring, W. ysgadan herrings; all perhaps akin to E. skate a
   fish.] (Zool.)
   Any one of several species of food fishes of the Herring
   family. The American species (Alosa sapidissima formerly
   Clupea sapidissima), which is abundant on the Atlantic
   coast and ascends the larger rivers in spring to spawn, is an
   important market fish. The European allice shad, or alose
   (Alosa alosa formerly Clupea alosa), and the twaite shad
   (Alosa finta formerly Clupea finta), are less important
   species. [Written also chad.]
   [1913 Webster]

   Note: The name is loosely applied, also, to several other
         fishes, as the gizzard shad (see under Gizzard),
         called also mud shad, white-eyed shad, and winter
         shad.
         [1913 Webster]

   Hardboaded shad, or Yellow-tailed shad, the menhaden.

   Hickory shad, or Tailor shad, the mattowacca.

   Long-boned shad, one of several species of important food
      fishes of the Bermudas and the West Indies, of the genus
      Gerres.

   Shad bush (Bot.), a name given to the North American shrubs
      or small trees of the rosaceous genus Amelanchier
      (Amelanchier Canadensis, and Amelanchier alnifolia).
      Their white racemose blossoms open in April or May, when
      the shad appear, and the edible berries (pomes) ripen in
      June or July, whence they are called Juneberries. The
      plant is also called service tree, and Juneberry.

   Shad frog, an American spotted frog (Rana halecina); --
      so called because it usually appears at the time when the
      shad begin to run in the rivers.

   Trout shad, the squeteague.

   White shad, the common shad.
      [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Chad \Chad\, n.
   See Shad. [Obs.]
   [1913 Webster]

WordNet (r) 3.0 (2006):

chad
    n 1: a small piece of paper that is supposed to be removed when
         a hole is punched in a card or paper tape
    2: a lake in north central Africa; fed by the Shari river [syn:
       Lake Chad, Chad]
    3: a landlocked desert republic in north-central Africa; was
       under French control until 1960 [syn: Chad, Republic of
       Chad, Tchad]
    4: a family of Afroasiatic tonal languages (mostly two tones)
       spoken in the regions west and south of Lake Chad in north
       central Africa [syn: Chad, Chadic, Chadic language]

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

chad
perf
selvage
snaf

    /chad/ (Or "selvage" /sel'v*j/ (sewing and
   weaving), "perf", "perfory", "snaf").  1. The perforated
   edge strips on paper for sprocket feed printers, after they
   have been separated from the printed portion.

   The term perf may also refer to the perforations themselves,
   rather than the chad they produce when torn.

   [Why "snaf"?]

   2. (Or "chaff", "computer confetti", "keypunch droppings") The
   confetti-like bits punched out of punched cards or paper
   tape which collected in the chad box.

   One of the Jargon File's correspondents believed that "chad"
   derived from the chadless keypunch.

   [Jargon File]

   (1997-07-18)


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

chad
 /chad/, n.

    1. [common] The perforated edge strips on printer paper, after they have
    been separated from the printed portion. Also called selvage, perf, and
    ripoff.

    2. The confetti-like paper bits punched out of cards or paper tape; this
    has also been called chaff, computer confetti, and keypunch droppings. It's
    reported that this was very old Army slang (associated with teletypewriters
    before the computer era), and has been occasionally sighted in directions
    for punched-card vote tabulators long after it passed out of live use among
    computer programmers in the late 1970s. This sense of ‘chad’ returned to
    the mainstream during the finale of the hotly disputed U.S. presidential
    election in 2000 via stories about the Florida vote recounts. Note however
    that in the revived mainstream usage chad is not a mass noun and ‘a chad’
    is a single piece of the stuff.

    There is an urban legend that chad (sense 2) derives from the Chadless
    keypunch (named for its inventor), which cut little u-shaped tabs in the
    card to make a hole when the tab folded back, rather than punching out a
    circle/rectangle; it was clear that if the Chadless keypunch didn't make
    them, then the stuff that other keypunches made had to be ‘chad’. However,
    serious attempts to track down “Chadless” as a personal name or U.S.
    trademark have failed, casting doubt on this etymology — and the U.S.
    Patent Classification System uses “chadless” (small c) as an adjective,
    suggesting that “chadless” derives from “chad” and not the other way
    around. There is another legend that the word was originally acronymic,
    standing for “Card Hole Aggregate Debris”, but this has all the earmarks of
    a backronym. It has also been noted that the word “chad” is Scots dialect
    for gravel, but nobody has proposed any plausible reason that card chaff
    should be thought of as gravel. None of these etymologies is really
    plausible.

    [74-12-31]

    This is one way to be chadless.