The prevention of an mRNA molecule from being translated into a protein by hybridizing it to its corresponding cDNA or to a complementary mRNA. This is used to identify cDNA molecules -- the scientist puts the cDNA molecule in question in a test tube with a number of mRNA molecules and observes which protein is no longer able to be made.
From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.