Arroba was a Spanish and Portuguese customary unit of weight, mass or volume. Its symbol is @. In weight it was equal to 25 pounds (11.5 kg) in Spain, and 32 pounds (14.7 kg) in Portugal.
The unit is still used in Portugal by cork merchants, and in Brazil by cattle traders. The modern metric arroba used in these country life activities is defined as 15 kilograms (33 lb).
In Peru the arroba is equivalent to 11.5 kilograms (25 lb).
In Bolivia nationally it is equivalent to 30.46 litres (6.70 imp gal; 8.05 US gal). However locally there are many different values, ranging from 11.5 litres (2.5 imp gal; 3.0 US gal) in Inquisivi to 16 litres (3.5 imp gal; 4.2 US gal) in Baures.
The at sign, @, normally read aloud as "at", also commonly called the at symbol or commercial at, and less commonly a wide range of other terms, is originally an accounting and commercial invoice abbreviation meaning "at the rate of" (e.g. 7 widgets @ £2 = £14). In recent years, its meaning has grown to include the sense of being "located at" or "directed at", especially in email addresses and social media, particularly Twitter.
It was not included on the keyboard of the earliest commercially successful typewriters, but was on at least one 1889 model[5] and the very successful Underwood models from the "Underwood No. 5" in 1900 onward. It is now universally included on computer keyboards. The mark is encoded at U+0040 @ commercial at (HTML: @).
The fact that there is no single word in English for the symbol has prompted some writers to use the French arobase or Spanish and Portuguese arroba—or to coin new words such as asperand, ampersat or apetail—but none of these has achieved wide currency.
@ is used in various programming languages although there is not a consistent theme to its usage.