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1.
This is a term used to describe women who only lie down silently during sex (and let their partner(s) do all the work).

Known in Japan as ‘maguro-onna’, which literally means ‘tuna woman’.
P1: Hey, how's your new girlfriend?
P2: Oh, she's the biggest tuna women I have ever known...
P1: Bummer.
by Wonderbagel September 14, 2013