Classification based on overall similarity in as many characters as possible, usually without weighting.
An approach to taxonomy based on measurable similarities and differences in phenotypic characters, but without consideration of homology, analogy, or phylogeny. Numerical taxonomy, where many, many characters are measured on all taxa, is a form of phenetics.
Phenetics is a method of attempting to classify biological organisms that does not use genetic or evolutionary information; it was invented by Sokal and Sneath in 1963. In a phenogram, organisms are grouped by superficial overall similarity. Phenetics was abandoned by most scientists in the 1980's because its classifications were arbitrary, mostly useless, and unstable. Paul Ehrlich was a proponent of this system.