The classic Western standard of male beauty, note the hunk is two things: handsome and manly.
His face tends to be squarish and sharp-featured, often with a prominent chin. He has big, well-muscled arms and a large torso with a slim waist with pronounced muscles. He also has fairly thick, muscular legs, though they get less attention. It is often implied that he is as well-endowed between the legs as in the arms. The hunk may or may not have body hair, depending on the time period, and facial hair is negotiable. Guaranteed, however, to adopt Perma-Stubble during his choice moments as Mr. Fanservice.
Clothing tends to be simple and timeless. Nowadays, a hunk's casual wardrobe will consist of tight jeans and either a tank top, tight T-shirt, or flannel shirt (if he wears one at all...works oriented to a female audience have him not in increasing numbers). For work and formal events, a smart suit is a given.
The hero of a story, if male, is frequently a hunk, particularly in an action series. If the lead character is a woman, the leading man or the heroine's Love Interest, if not both, tends to be a hunk.