Someone who is well built, that has ripped muscles, along with a buff, toned body structure. Not necessarily a body builder, though obviously someone who takes care of their body, through exercise.
Generally in reference to males, that have a well built and honed body.
Also has been in reference to a pornography genre, where the men are specially chosen, for their ripped muscles, and buff body.
Beefcake Men, are considered to be not just well built, but have good looks to compliment their body shape.
These types, also generally, enjoy displaying their physical attributes, to willing viewers.