The '@' symbol is officially called the 'commercial at'.
Why it is true
Historically, it was used in commerce to mean 'at the rate of'. It only became popular for email addresses in 1971 by computer scientist Ray Tomlinson.
Source: Technology History
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.