vegetarianism or veganism. As such, the term pollo-vegetarian (which is sometimes used to describe the diet) is a misnomer because vegetarians do not eat any animal meat; the term pollotarian is accurate.
The word pollo is derived from the Latin for chicken. "Pesce-pollotarianism" (or chickifishitarian) is a pejorative neologism that means one who includes both chicken and fish in their diets as well as non-meats, but pescetarianism and pollotarianism are separate entities.
There are many rationales for maintaining a pollo-vegetarian diet. One is that of health, based on findings that red meat is detrimental to health in many cases due to non-lean red meats containing high amounts of saturated fats.
For some the rationale is ethics: believing that either the treatment, or simply the killing and eating, of mass market "meat" mammals is unethical. The rationalization for eating chickens in this case is usually either "I have to eat some kind of meat" (see complete protein) or "chickens are less intelligent than other animals".