doctrine of equivalents

A legal docrine that allows a court to expand the literal language of claims so that one who has made inconsequential changes in the product or process to avoid infringement will nevertheless be found to be infringing.

One literally infringes a claim where every element of the claim is expressly satisfied by a device, process, or composition of matter. Under the judicially created doctrine of equivalents, one may be held liable as an infringer even if one does not literally infringe a patent. In general, it is an equitable concept employed to prevent someone from getting the benefit of the invention by making a minor change that avoids literal infringement. See also the related concept of file wrapper estoppel.

a judicially created theory for finding patent infringement when the accused process or product falls outside the literal scope of the patent claims. The essential objective inquiry is: "Does the accused product or process contain elements identical or equivalent to each claimed element of the patented invention?"

-- see MPEP 2186 for more