"Dual" meaning more meat than a leghorn is my definition of what I consider dual. Take it or leave it, but as far as I know, in general people consider "dual" types as anything with some meat on the bones. They still use the term "dual" in stuff like the Henderson's breed chart, so who knows.
http://www.ithaca.edu/staff/jhenderson/chooks/chooks.html
There are a few on there which have been moved from "meat" to "dual" like Langshans, and most "dual's" sold by hatcheries tend to be more "layer" b/c they breed for eggs to hatch to have chicks to sell.
Type: Breeds can also be separated by the purpose for which they were originally developed. Dual Purpose were develped for both meat and eggs. These days, most of these breeds are only found in backyards and small farms. [formerly Meat] indicates that in the days before Cornish X Rock dominance (post World War II), this breed was highly prized as a meat bird. Layers are those breeds that are principally used for egg production. As a general rule these birds are active and lively, lighter in weight than most other standard breeds, and not broody. Game breeds were once bred for cockfighting. It is believed they were the first chickens to be bred by humans. As a general rule, they are noisy and pugnacious, but some can be docile toward toward humans, and hens can be very protective mothers. As a rule they have low egg production. Fancy breeds are those with special features, such as crests, feathered feet, unusual colors, beards, muffs, or five toes. Some fancy breeds are strictly ornamental, but many others are will also be found among the layer and dual purpose breeds, as well. Bantam breeds are little birds of ornament and pleasure. The term bantam comes from a small chicken that originated in the Bantam region of Java, but after they were introduced to Europe centuries ago, any small variety of fowl was called a bantam. Bantams include both miniature versions of the large standard breeds and True Bantams, breeds for which there is no matching large standard. The descriptive term True, however, does not mean a naturally diminutive breed, since many True Bantams have been highly engineered by breeding programs.
Maybe in enough years the known term of dual will change.
