Levels of formality, traditionally defined

There seems to be a lot of confusion in the definitions of clothing formality these days. I've heard a lot of misused terms both in everyday life and bandied about on internet forums and chat rooms. A suit is called anything from "business dress" to "semi-formal" or "formal." Some people even call a blazer and chinos semi-formal!

I won't get into womenswear here, because I'm not completely solid on which dresses are appropriate to each level of formality.* In any case, it can get frustrating when you or the host/employer don't really know what's what.

To clear things up for both parties, here are the definitions from most to least formal. I'll try not to be too wordy here.

Formal: During the day, a morning coat. At night (after six), white tie.

Semi-Formal: During the day, a stroller coat (scroll to bottom). At night, black tie.

Informal: A suit and tie. This is the same as "business dress" or "cocktail attire" (think of Don Draper sipping a martini). Outside the office or at more artistic places of employment, one is generally free to express a little more individuality in their patterns, colours, and accessories.

Casual: This is NOT to be confused with the above. Technically, sport coat and tie or a little below falls into this category. "Business casual" originally meant the former, though the term has been grossly misappropriated in the last two decades to include jeans, t-shirts, and sneakers.

Understandably, some clothing aficionados want to differentiate anything involving the aforementioned items as "streetwear" or "ultra-casual" given the alarming rise in these items worn anywhere from nice restaurants (ugh, why?) to funerals (yes, I'm serious).

Worst comes to worst, just ask your host or employer exactly what they mean. They usually -- and shouldn't -- mind explaining.

Hope this helps anyone.

*If anyone wants to explain this for me, I'd be grateful.