The "At Sign" (@) is a symbol used primarily in email addresses to separate the user's name from the domain name. For example, in the email address user@example.com, "user" is the local part, and "example.com" is the domain. This format helps route emails to the correct destination on the internet. Originally used in accounting and commerce to denote "at the rate of," the @ symbol gained popularity with the rise of email in the 1970s. It was first used in this context by Ray Tomlinson, a computer engineer who sent the first email using the symbol to connect users with different computers.