The at-sign (@) is a symbol. It is used in bills, emails and programming. In email, it is used to show a specific domain of an email address. In bills, it used to mean "at a rate of"; for example, "7 widgets @ £2 = £14". In programming, the at-sign has been used in a wide range of programming languages. It was invented by Ray Tomlinson.
The sign is one of several special symbols on the standard English keyboard.