On the Internet, @ (pronounced "at" or "at sign" or "address sign") is the symbol in an e-mail address that separates the name of the user from the user's Internet address, as in this hypothetical e-mail address example: firstname.lastname@example.org.
In business, @ is a symbol meaning "at" or "each." For example, it means "each" in "4 apples @ $.35 = $1.40." Perhaps because it was one of the standard characters designed into typewriters (usually with the upper shift key pressed), the @ was chosen for inclusion as one of the special characters in the ASCII set of characters that became standard for computer keyboards, programs, and online message transmission. In July, 1972, as the specifications for the File Transfer Protocol (FTP) were being written, someone suggested including some e-mail programs written by Ray Tomlinson, an engineer at Bolt Beranek and Newman, chief contractor on ARPANet (Advanced Research Projects Agency Network), the precursor of the Internet. In their book, Where Wizards Stay Up Late, Katie Hafner and Matthew Lyon describe how the @ sign got there:
Tomlinson....became better known for a brilliant (he called it obvious) decision he made while writing [the e-mail] programs. He needed a way to separate, in the e-mail address, the name of the user from the machine the user was on. How should that be denoted? He wanted a character that would not, under any circumstances, be found in the user's name. He looked down at the keyboard he was using, a Model 33 Teletype, which almost everyone else on the Net used, too. In addition to the letters and numerals there were about a dozen punctuation marks. "I got there first, so I got to choose any punctuation I wanted," Tomlinson said. "I chose the @ sign." The character also had the advantage of meaning "at" the designated institution. He had no idea he was creating an icon for the wired world.