I have heard that on farms chickens are called broilers. Why?

The term ‘broiler’ is a simplification from the 1950s, a time when professional chicken farming was beginning to develop in America. Faced with the need to indicate the ultimate purpose of raising chickens as opposed to others, since most people in America consumed their chickens (still do today) by cooking them on the grill… so broiler became commonly used among breeders and is now a term that has become fixed in poultry jargon.