A sexually attractive and muscular man.
Hunks are men who are attractive and well-built beyond the average guy. A lot of soap opera actors are considered hunks as are Playgirl models and Abercrombie models. Hunks are not necessarily bodybuilders but they must have a defined form and a very attractive face and presentation.
The term hunk seems to have appeared in the early 1800s and is probably taken from the Flemish hunke, which means piece of food.
Television shows and movies try and star or at least co-star hunks in their shows because their desirability will bring more viewers. Hunks are often used on commercials and magazine ads in the same way bikini models and centerfolds are used. Because both men and women are attracted to hunks, they are considered trophy boyfriends and are often very popular. In porn, a hunk is generally a guy with a well developed chest and preferably well hung, but face and attitude as well as body plays a part in being a hunk.
Hunk can also mean a piece or chunk of something like a hunk of cheese.