It is read as at, but the symbol itself has no proper name in English. The at symbol seems to be the only generally recognized way of referring to it.
Traditionally it was used in financial records to show the price of a particular item on a list, and read as at:
50 units @ £4.75
Now it has found a new life as the symbol that joins the name of a person or a department in an organization to a domain name to make an email address:
dictionary@cambridge.org (read as dictionary at cambridge dot org)
It is also used in microblogging and social media, for example on Twitter, before the username, so that publicly readable replies can be sent:
@CambridgeWords
The symbol originated in Spain, where it is called arroba, from an Arabic word for a standard weight. Many languages use an animal name to refer to the letter. It can be a snail (Italian and Welsh), a monkey (Polish and Bulgarian), a mouse (Chinese), a duck (Greek), or a dog (Russian and many languages of the former Soviet Union). It can also be a local foodstuff: rollmops in Czech and Slovak, strudel in Hebrew, or various curl-shaped pastries in Catalan, Bulgarian, and Swedish. The most poetic is perhaps moon’s ear in Kazakh. Various suggestions have been made for English (mostly rather less poetic), including arobase (from French) asperand, ampersat, and astatine – but none of these has caught on. Two of these are based on ampersand, the & symbol that was originally a way of writing et (“and”) in Latin.
Symbols that represent ideas in this way are called ideograms (or ideographs), although it could be argued that @ and & represent words, rather than ideas. Other ideograms include our numerals 0 – 9, the recycling symbol ♻, and many Chinese characters and ancient Egyptian hieroglyphs.
Several other exotic typographical symbols have recently entered the Cambridge dictionary, thanks to their use in internet communication and computer programming. These include angle brackets: <> ; pipe | ; backtick ` ; hash # (also called the pound sign in North America); and caret ^. Forward slash / and backslash \ are also fairly recent arrivals – slash used to be called stroke or oblique in British English.
All are to be found on your computer keyboard, although you probably use them less than @.