The Collaborative International Dictionary of English v.0.48:

Indentation \In`den*ta"tion\, n.
   1. The act of indenting or state of being indented.
      [1913 Webster]

   2. A notch or recess, in the margin or border of anything;
      as, the indentations of a leaf, of the coast, etc.
      [1913 Webster]

   3. A recess or sharp depression in any surface.
      [1913 Webster]

   4. (Print.)
      (a) The act of beginning a line or series of lines at a
          little distance within the flush line of the column or
          page, as in the common way of beginning the first line
          of a paragraph.
      (b) The measure of the distance; as, an indentation of one
          em, or of two ems.
          [1913 Webster]

   Hanging indentation, or Reverse indentation, indentation
      of all the lines of a paragraph except the first, which is
      a full line; also called a hanging indent.
      [1913 Webster]

The Free On-line Dictionary of Computing (17 December 2009):

indentation
indent

    Space and/or tab characters
   added at the beginning of one or more consecutive lines to
   indicate the structure of a piece of text, e.g.  indenting a
   passage to make it stand out.

   Indentation is important in source code for readability.
   See indent style.  Some programming languages go further and
   use indentation as the main method to represent block
   structure to the compiler or interpreter, see off-side
   rule.

   (2008-10-23)


Moby Thesaurus II by Grady Ward, 1.0:

91 Moby Thesaurus words for "indentation":
   alveolation, alveolus, blaze, boss, bump, cleft, colophon,
   concavity, convexity, crena, cut, dactylogram, dactylograph, dent,
   depression, digging, dimple, dint, embossment, engraving,
   excavation, excrescence, feel, fingerprint, finish, footmark,
   footprint, footstep, fossil footprint, furrow, gash, gouge, grain,
   granular texture, hack, hollow, honeycomb, ichnite, ichnolite,
   impress, impression, imprint, incision, indent, indention,
   indenture, jag, jog, joggle, kerf, knub, lump, mark, mining, nap,
   nick, nock, notch, nub, pad, paw print, pawmark, pile, pimple, pit,
   pock, pockmark, print, protuberance, pug, pugmark, score, scotch,
   seal, shag, sigil, signet, stamp, step, structure, stud,
   sunken part, surface, surface texture, texture, thumbmark,
   thumbprint, vestige, wale, weave, woof