The @ symbol in email addresses was chosen because it was rarely used for anything else.

In 1971, engineer Ray Tomlinson was working on a way to send messages between separate computers on ARPANET, the precursor to the internet. He needed a character to separate a user’s name from the name of the machine they were on, and picked the @ symbol specifically because it didn’t already appear in any personal or computer names, avoiding ambiguity.

The symbol had existed on typewriter and computer keyboards for decades before that, mostly used in commercial pricing to mean “at the rate of,” but Tomlinson’s choice gave it an entirely new, far more widely used meaning. He later said he had no idea at the time that the format would still be in use everywhere decades later.