Its meaning is certainly known by all, as are many (most?) slang terms (do I really need to list some? ).....but slang it is.
A strobe is a light that flashes over and over at intervals of a set length. While they are used for photographing and for other things, the electronic flash units that are designed as photographic equipment are not designed for use as strobes, and are not used as strobes when used the way that most photographers use them (i.e., when they fire only when you tell them to fire, and at no other time). If you were to rig up something that set your flashes to fire at evenly spaced intervals, or even if you were to do it manually with a stopwatch and the dump button, then you would have a strobe, in the technical sense.
...but my point was really that this does not have to do with nationality. In the U.S.A. or Britain, "strobe" to mean any electronic flash unit is slang terminology. A "strobe" is a timed repeating light in both British English and U.S. English, and it is slang for electronic flash units in both British English and U.S. English. I know for a fact that British people use the term. Additionally, even if the slang term "strobes" to mean any electronic flash is more prevalent in the United States than in Britain, it does not mean that it is not slang here in the U.S.A.