That’s a new term I heard, invented by Hope Smith (though others might well have anticipated it) — though of course there’s nothing new about the actual phenomenon.
The analogy is to “business casual,” and the meaning is clothing that tries to be sexy — not just good-looking or elegant, but sexy — in a way that is compatible with mainstream business or professional jobs, and even advances the wearer’s business goals. Business-to-business salespeople might, for instance, dress “business sexual” to catch the buyer’s attention, but not so much as to undermine the credibility of the product. Business lawyers might do the same, though I suspect that’s much riskier for them. My sense is that doctors would be wise to avoid business sexual as much as possible, though I might be wrong (for instance, perhaps there are some extremely subtle forms of business sexual that would work for them).
I think the term makes the most sense for jobs that are “business” in the sense in which “business” is used in “business casual” — more traditional white-collar business or professions, often ones that sell to other businesses and not just (say) retail, waiting tables, and so on. You can only dress “business sexual” in the sort of job where you can imagine someone telling you that you can dress “business casual”; there are no “business sexual”-dressed lifeguards or strippers.
Naturally, all the examples that come to my mind are of women, but I can’t say whether this is because of reality (sexy dressing is more effective for women than for men) or because of me (I notice it when women do it and not when men do it). In any case, I liked the label, so I thought I’d pass it along.
UPDATE: Just to make it clear, the term isn’t meant to refer to clothing that would normally be seen as (for want of a better term) “slutty”; business sexual clothing might be no more revealing, for instance, than clothing that would be seen as quite appropriate at a party. Rather, it’s clothing that infuses some extra sexuality — often in an attempt to yield a business advantage — that is not normal in business clothing but that would not normally be seen as unduly immodest or forward in social clothing.