It's a setting for "can impregnate/be impregnated", so it's not explicitly transing. But it's now en vogue to call sims "masculine frame", or "feminine frame" instead of just male or female. It also kind of cracked me up that when they introduced this feature they put a "non binary" sim in the next game pack - "masculine frame" with a preference for "feminine" clothing, okay, whatever, it's a good thing you can pick any clothes for your sim... but also unable to impregnate or be impregnated. I thought the implication that being non binary is the same as being sterile was definitely interesting. The insane Sims community didn't have an issue with that, though. I guess unsurprising from a group that were less upset that 17 pride flags were introduced but no lesbian flag than that you can't somehow assign neopronouns to your sim (which... How would that work when they don't even speak English???)