That little a with a circle curling around it that is found in email addresses is most commonly referred to as the at symbol.
小写字母a外加个圆圈，这一符号常出目前email（邮件）地址中，一般是作为at的标记。

Surprisingly though, there is no official, universal name for this sign. There are dozens of strange terms to describe the @ symbol.
然而让人感到惊奇的是，这一标记居然没官方的，通用的名字。有几十个奇怪的术语用来描绘@这一符号。

Before it became the standard symbol for electronic mail, the @ symbol was used to represent the cosplayt or weight of something. For instance, if you purchased 6 apples, you might write it as 6 apples @ $1.10 each.
@这一符号在成为邮件的规范符号之前，曾被用来表示物品的单价或水平。比如，你买6只苹果。就能写成六只苹果，每只@$1.10，表示每只苹果1.10USD。

With the introduction of e-mail came the popularity of the @ symbol. The @ symbol or the at sign separates a person's online user name from his mail server address. For instance, Its widespread use on the Internet made it necessary to put this symbol on keyboards in other countries that have never seen or used the symbol before. As a result, there is really no official name for this symbol.
伴随邮件的用法，@这一符号愈加普及了。符号@或'at'标记将上网用户的名字与其邮件的服务器地址分开。比如：xxxxxx。 这一符号在因特网上的广泛用使得很多以前从未见过或用过它的国家需要在它们的电脑键盘上加上这一符号键，结果导致这一符号并没真的的官方名字。

The actual origin of the @ symbol remains1 an enigma2.
@符号的确切起源仍然是谜。

History tells us that the @ symbol stemmed from the tired hands of the medieval monks3. During the Middle Ages before the invention of printing presses, every letter of a word had to be painstakingly4 transcribed5 by hand for each copy of a published book. The monks that performed these long, tedious copying duties looked for ways to reduce the number of inpidual strokes per word for common words. Although the word at is quite short to begin with, it was a common enough word in texts and documents that medieval monks thought it would be quicker and easier to shorten the word at even more. As a result, the monks looped the t around the a and created it into a circle-eliminating two strokes of the pen.
历史告诉大家，@这一符号起来自于中世纪僧侣疲劳的双手。中世纪时印刷机尚未创造，要出版一本书，每个单词的每个字母都得用手工辛苦的刻出来。从事这项长期辛苦誊写刻画的僧侣们就开始探寻降低每个常用字笔画数的办法。虽然at这一单词开始写起来非常短，但它在文本和文件中频繁出现。中世纪的僧侣们就想到假如能进一步简化它，就能写起来更快更容易。结果，僧侣们就在a四周画了一个圈，从而省却了字母t的两个笔划