Southern blot: A test commonly used in molecular biology and genetics, the purpose of the test being to check for a match between DNA molecules.
In the Southern blot technique, DNA fragments are separated by a method called agarose gel electrophoresis, transferred (blotted) onto membrane filters, and hybridized with complementary radiolabeled probes. The aim is to detect specific base sequences with the probes.
Lest all of this sound esoteric, note that in the television series "The X Files" a Southern blot was done (in this case, to learn if some alien virus genome had been integrated into a person's genome).
The Southern blot is named after its inventor, the British biologist M.E. Southern. There is also a Northern blot and a Western blot.