At

At is a common English preposition used to indicate a location, a point in time, or a specific target. It appears in phrases such as at the door, at noon, and at 5 percent. In mathematics, computing, and indexing, the word is used to denote precise points or positions, and in some programming languages it participates in various notational contexts.

Astatine (symbol At) is a chemical element in the halogen group with atomic number 85. It is extremely rare in nature and highly radioactive; no stable isotopes exist. Astatine is produced artificially in particle accelerators or nuclear reactors. Its short half-lives and scarcity limit practical applications, though it has been studied for potential use in targeted radiotherapy and nuclear medicine research.

AT is the ISO 3166-1 alpha-2 code for Austria, and the country’s internet top-level domain is .at.

The at sign, represented as @, is widely used in email addresses, where it separates the local part from the domain name, and in social media handles to indicate user accounts. It was introduced into electronic mail in 1971 by Ray Tomlinson.