What is “?

. is most commonly understood to be a period, also known as a full stop. It's a punctuation mark used to indicate the end of a declarative sentence. You can read more about its general use in punctuation.

In computing, the period also has significant roles. For example, it's used in file extensions, such as .txt or .jpg. This usage helps the operating system identify the file type. Furthermore, periods are commonly used in URLs to separate domain names and top-level domains (TLDs), such as .com or .org. It may also appear in programming languages, frequently used to access properties or methods of an object.