Usually the present-tense form of "to gains" or "to garans", but it can be used as both a verb and a noun, respectively.
V: To engage with, sexually.
N: One who is always wholeheartedly open to engaging sexually, although not necessarily a slut.
"Man, I totally want to geenz that chick, her ass is epic."
"That girl is a total geenz, DTF all day erryday."