Boots are distinguished by their taller design, with a boot "shaft" that encloses the ankle. Take away this boot shaft, and you would be left with a regular shoe.
Nothing else can characterize such a broad category as "boots." The popularity and design variety of boots make them one of the most common, and diverse, categories of men's footwear, containing vastly different styles such as chelsea boots, derby boots, chukka boots, and button boots.