The Collaborative International Dictionary of English v.0.48:

electrophoresis \electrophoresis\ n.
   1. (Chem.) the motion of charged molecules or particles in a
      liquid medium under the influence of an electric field;
      particles with a positive charge move toward the cathode
      and negative to the anode. [WordNet sense 1]

   Syn: cataphoresis.
        [WordNet 1.5]

   2. (Chem., Biochem.) the application of the principle of
      electrophoresis to separate molecules, used as an
      analytical or preparative technique; as, separation by
      electrophoresis; gel electrophoresis.
      [PJC]

   Note:

   Gel electrophoresis is a technique in which the molecules
      to be separated are moved through a gelatinous medium
      under the influence of an electric field. At the
      completion of a period of electrophoresis, the gel, unlike
      a liquid solution, may be manipulated as a single object,
      permitting the substances contained within to be detected
      or visualized by a variety of methods, and their relative
      mobilities determined. It is therefore a popular analytic
      tool in biochemistry, and has many variants. Popular
      substances used to create the gel are starch,
      polyacrylamide, and agarose. Since a polyacrylamide gel
      can be created with different concentrations and different
      degrees of cross-linking, the pore size of the gel can be
      controlled to provide special properties appropriate to
      separation of specific molecules, as for example
      optimizaion for separation within a particular molecular
      weight range. in SDS-polyacrylamide gel electrophoresis,
      SDS (sodium dodecyl sulfate, a detergent) is included;
      it binds to and denatures protein molecules, allowing them
      to be separated on the basis of their molecular weight
      alone. It is thus used as one method of determining the
      molecular weights of isolated protein chains.
      [PJC]