1. Biotechnology is a set of powerful tools that employ living organisms  (or parts of organisms) to make or modify products, improve plants or animals,or develop microorganisms for specific uses. Examples of the "new biotechnology" include
the industrial use of recombinant DNA, cell fusion, novel bioprocessing techniques, and bioremediation.
-- National Agricultural Library

2. The use of microorganisms, such as bacteria or yeasts, or biological substances, such as enzymes, to perform specific industrial or manufacturing processes. Applications include the production of certain drugs, synthetic hormones, and bulk foodstuffs as well as the bioconversion of organic waste and the use of genetically altered bacteria in the cleanup of oil spills.
--The American Heritage Dictionary of the English
  Language, Fourth Edition

3. The industrial use of living organisms or biological techniques
developed through basic research. Biotechnology products include antibiotics, insulin, interferon, recombinant DNA, and techniques such as waste recycling. Much older forms of biotechnology include bread making, cheese making and brewing wine and beer.
-- Biotech Life Sciences Dictionary

4. Biotechnology: The scientific manipulation of living organisms, especially at the molecular genetic level, to produce useful products. Gene splicing and use of recombinant DNA (rDNA) are major techniques used.
-- Charles Hagedorn and Susan Allender-Hagedorn,  An Agricultural and Environmental Biotechnology  Annotated Dictionary, Virginia Tech University
What is Biotechnology?