An acronym that stands for Estimated Time to Fuck. Used in time estimation on one think they will be able to fuck a particular person.
Guy 1: Wow that chick is really messy drunk, what do you think her ETF is?
Guy 2: I say cab ride
Guy1: So you still going out with that chick from J-date?
Guy2: Yes, my ETF is defiantly 4 dates and a meeting with the parents.
Fat chicks are known for their low ETF.