Chino The Modern Dress Pant

Chinos are trousers made of cotton twill (a specific type of weave), and have their roots in the British Army. Specifically what makes a Chino a Chino is:  The use of Chino cloth, a twill weave fabric made traditionally with 100% cotton (some cotton synthetic blends may be used) is what makes a Chino a Chino.  Most classifications of trousers are based on the material used (e.g. denim, a type of fabric, defines jeans, a type of trouser) and Chinos are no different.  If a pair of trousers uses a twill weave Chino fabric, it's a Chino.  Most Chinos use a medium weight twill between 7oz and 9oz
Chinos are a very useful piece of clothing because they are incredibly versatile - unlike many types of pants, they can be worn with professional and casual clothing easily.