The five levels of formality in a Gentleman's dress

1. Formal - this is what is also known as 'white tie'. No matter how often menswear companies refer to lounge suits and business shirts as being formal, they will always be wrong. White tie is well defined, for example here at the university of Cambridge website http://www.societies.cam.ac.uk/cuhags/whitetie/defn.htm. The shirt most definitely be white with a stiff (preferably removable) wing collar and a marcella front bib.

2. Semi-Formal - Black Tie. many will refer to this as formal dress, and that is because it is about as formal as they will ever wear. It is not formal. See http://en.wikipedia.org/wiki/Black_tie for a definition

3. Informal - This is where the lounge suit (or business suit) resides. That suit that you thought was a formal uniform is very informal in the hierarchy of gentleman's dress.

4. Casual - No not jeans and a Tee Shirt, but a sports jacket, tie and contrast trousers.

5. Sub-standard - this is what most people seem to wear regardless of the formality of an event these days. Jeans, T-Shirts, Short-sleeved shirts etc.