1. The naturally-occuring, normal, non-mutated version of a gene.
2. The original parent strain of a virus, bacteria, fruit fly, mouse, or other laboratory test organism. Often refers to how organisms are found naturally, in the wild, before mutations were induced by researchers.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.