EDIT Languages In e-mail addresses, the commercial at unambiguously seperates user from server names, e.g. \"johndoe@xyz.org\", which is why it is often used as a symbol for the Internet, an Internet café etc.

In the English speaking world, the use of this character is not restricted to the Internet. Thus, Adobe in its Photoshop programme in the top bar indicates the magnification level with \"imagexyz.jpg @ 200%\".

The English term commercial at or at sign translates into
German as Klammeraffe (spider monkey),
French as Arobe, Arrobe or Arrobas in France,
Hebrew as Strudel,
Chinese as xiao laoshu = little mouse or laoshu hao = mouse mark, and
Czech as zavináč = rolled pickled herring.

History
While the true origin of this character is shrouded in numerous myths, the at sign is definitely older than its world-wide success as the symbol of the generation @.
This character appeared on US American typewriter keyboards as early as at the end of the 19th century and has thence been included in the ASCII code. In search of an unambiguous character for the separation of user name from domain, a programmer by the name of Ray Tomlinson in the winter of 1971-72 came across the character on the keyboard of his TeleType33 as he was inventing the modern e-mail. At the time, Tomlinson was working at Bolt Beranek and Newman (BBN) who had been assigned to develop the predecessor of the Internet, ARPA-Net, by the ARPA office of the US Department of Defence.

There are at least two conclusive theories on the origin of this character:
a) The character is proved to have appeared in 1555 on the Iberian Peninsula as an abbreviation of the arroba, a unit of measurement of solids and liquids corresponding to about 10 kilogrammes or 15 litres. The word arroba originates from the Arabic ar-roub = the quarter. Until today, the commercial at is called arroba in Spanish and arrobas in French.

b) The character represents an Anglo-Saxon commercial symbol of the English \"at\" used like the French \"à\" for pricing goods, e.g. 5 apples @ 50 ¢ = 5 apples at 50 cents.

None of these theories necessarily excludes the other since, over the course of centuries, meanings may have shifted.

Another theory has, in the meantime, been disproved: that the character represents a ligature of the letters a and d in the Latin word \"ad\" (= to, towards). This version held a certain appeal since the shape of the minuscule d for some time did indeed suggest this interpretation. This shape exists until today as a mathematical character: ∂ U+2202 PARTIAL DIFFERENTIAL. No such ligature, however, has yet been found in any Latin manuscript.

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