Noun: Male cleavage, often seen when a button-down shirt is unbuttoned to an extreme. Generally viewed in nightclubs or on CSI. Word origin - the combination of "He" (as in "male") and "Cleavage" (as in "exposure of the upper boob area") hence "he-vage."
Did you see CSI last night? Warrick was sporting some serious HE-VAGE in the lab for some reason.