You've probably seen a Beaux-Arts building without knowing exactly what to call it: from c. 1880 - 1950 it was the default style for skyscrapers, large office buildings, and the like in the US, France
, and some other places. That is, if it's not plain Bauhaus
, or obviously Art Deco
or Art Nouveau
(though there was some overlap), it's probably "Bozar", in some way or another.
The style is named for L' Ecole des Beaux-Arts, in Paris, logically enough, and refers to its eclectic use of French architectural forms from the 16th- 19th centuries, though there may also be some Gothic and Neoclassicism mixed in -- it's that kind of style! Ornamentation, on the large and small level, abounds, floor plans are symmetrical, and usually include at least one cavernous public space (the lobby, though there may be restaurants, "winter gardens" or others) to carry the theme of overall grandeur indoors. At its best, a Beaux-Arts building is a total environment, where everything from the overall shape of the building to the lighting sconces to the design of the carpet carries out a theme, which can be as traditional as "Versailles", or as complex as "Modern Communication" (which, given the time, means switchboard telephony, telegraphy and radio.)
Mostly, it stayed the default because clients and the public loved it, but architects hated it, since it almost demanded a lot of extraneous (and expensive) fussy details, and its overall pattern for high buildings -- the ziggurat -- required that many interior walls carry the weight, not only of the building itself, but massive stonework as well. Oftentimes, because of its inherent expense, only the facade and lobby would be decorated, faux elements would predominate, and if badly done, it could be terribly, terribly ugly.
There are almost too many examples to name, but the best-known one is only one of the better ones -- The Empire State Building.