An "identifier" is a name or label used to uniquely distinguish an entity within a specific context. In programming, identifiers are used to name variables, functions, classes, and other elements, allowing developers to reference them easily. For example, in the programming language Python, a variable named "score" serves as an identifier for the value it holds. Identifiers must follow certain rules, such as starting with a letter or underscore and not containing spaces or special characters. They are case-sensitive, meaning "Score" and "score" would be considered different identifiers. Properly naming identifiers enhances code readability and maintainability.