Here's one point-of-view:
In the lexicon of gentlemen of means, the term 'dress shirt' is used exclusively to mean that type of shirt meant to be worn with a tuxedo. The term used by the same gentlemen for a shirt meant to be worn with a business suit is 'shirt'. Why? It is assumed that a gentleman will always be wearing a suit except on those occasions when he is wearing a 'white-tie shirt or a 'dress shirt' or a 'sport shirt' or a 'polo shirt' or a 'golf shirt'. Hence, the everyday term 'shirt' is used for the expected everyday wear. A 'sport shirt' is one which can be worn by itself. It has barrel cuffs rather than cuffs meant for cuff links and a different placement of the first center placket button. Most 'sport shirts' can also be worn with a blazer. If this sounds rather simplistic, so be it. The rules of etiquette don't often change in those circles where 'dress-down Fridays' are regarded as an unspeakable aberation of some third-world cult needing immediate extermination. Therefore, as previously implied by other posters, this thread is rather . . . stupid
. One cannot make out-of-context determinations in this instance. Each social circle in which a particular garment is worn has its own rules governing such wear. If your favorite musical group is Megadeth, I would assume that your idea of 'dress shirt' would be that one of your leather vests which actually closes in the front.
Please do not play on word when you know what I mean. So if you prefer answer to this question : "what is a business shirt" ? I am French, I use a language which is not mine. So if saying "dress" instead of "business" (everybody BUT you understand the question) is being stupid, what are people here who do not even speak a word in French?