shim

from The Collaborative International Dictionary of English v.0.48

Shim \Shim\, n.
   1. A kind of shallow plow used in tillage to break the
      ground, and clear it of weeds.
      [1913 Webster]

   2. (Mach.) A thin piece of metal placed between two parts to
      make a fit.
      [1913 Webster]

from Jargon File (4.4.4, 14 Aug 2003)

shim
 n.

   1. A small piece of data inserted in order to achieve a desired memory
   alignment or other addressing property. For example, the {PDP-11} Unix
   linker, in split I&D (instructions and data) mode, inserts a two-byte
   shim at location 0 in data space so that no data object will have an
   address of 0 (and be confused with the C null pointer). See also
   {loose bytes}.

   2. A type of small transparent image inserted into HTML documents by
   certain WYSIWYG HTML editors, used to set the spacing of elements
   meant to have a fixed positioning within a TABLE or DIVision. Hackers
   who work on the HTML code of such pages afterwards invariably curse
   these for their crocky dependence on the particular spacing of
   original image file, the editor that generated them, and the version
   of the browser used to view them. Worse, they are a poorly designed
   {kludge} which the advent of Cascading Style Sheets makes wholly
   unnecessary; Any fool can plainly see that use of borders, layers and
   positioned elements is the Right Thing (or would be if adequate
   support for CSS were more common).

from The Free On-line Dictionary of Computing (8 July 2008)

shim

   <jargon, memory management> A small piece of data inserted in
   order to achieve a desired {memory alignment} or other
   addressing property.

   For example, the {PDP-11} {Unix} {linker}, in split I&D
   (instructions and data) mode, inserts a two-{byte} shim at
   location 0 in data space so that no data object will have an
   address of 0 (and be confused with the {C} null pointer).

   See also {loose bytes}.

   [{Jargon File}]

   (1994-12-21)