Sorry, someone probably asked this before, but I can’t search it.
What is “@” called?
Masterspace.
It is the “at” sign.
“at-sign”. 
It gets more interesting in other languages. In Esperanto, for instance, it is sometimes called “heliko” (snail), but it is only rarely used.
The Jargon File on the at-sign and other symbols.
Man that is pretty obscure. I did a search for masterspace ascii and got only about 10 results. The ones I looked at said @ was masterspace. I don’t think I have ever seen such a low turnout for a computer related search ever. It does not appear to be a typesetting convention.
In Spanish it’s an “arroba,” actually a somewhat archaic unit of weight or volume. The term was revived when the @ sign became prevalent in computerese.
Depending on your usage of the symbol, this link should assist.
Esperanto is rarely used, that is… 
I’ve been agitating for “appersat,” by analogy with “ampersand.”
In Hebrew it’s known as a “strudel.” Seriously.
The a is for apple?
In Dutch it’s officially called “monkey’s tail”. I kid you not.
Me: “Could you spell that e-mail adress for me, please?”
Receptionist: “Sure. That’s S-M-I-T-H monkey’s tail hotmail.com”.
I read some where that some peeps call it a spider-monkey. At sign works for me however.
In danish it’s “snabel-a”, snabel=elephants’ trunk.
-Tikster
Unrelated, but in elementary school I misheard a teacher and for years afterwards thought that the symbol # was called a ‘palensine’ (not ‘pound sign’.)
In Polish it’s malpa (with a line through the ‘l’), which means “monkey.”
In Hungarian it’s kukac, which means “maggot” or “worm.”
It’s called the “at sign” , as noted above.
I one of his novels (The Demolished Man, I think), Alfred Bester imagines a future society in which @ and & have replaced their phonetic equivalents, so that the name “Atkinson” becomes “@kinson” and “Wiegand” becomes “Weig&”. I doubt if it would really happen, but it’s a cute literary pyrotechnic trick.
Before we had internet addresses to provide a use for “@”, it used to be used to convey rates:
“5 bushels of apples @ $10 each”, and so on.
Speaking as a typsetter, we always refer to it as an “at” symbol.
You mean the at sign was used to mean “at”? And then email came along and totally revolutionized everything by using it to mean “at”? Gosh, whodathunkit. This is why I love the Straight Dope.
Or a hash sign even, I’ve heard that # is used sometimes in the US to denote £GBP but I can’t see why 