Identifiers are names used in programming to uniquely identify variables, functions, classes, and other entities. They help programmers reference specific elements in their code, making it easier to read and maintain. Identifiers can consist of letters, digits, and underscores, but they must start with a letter or an underscore. In many programming languages, such as Python and Java, identifiers are case-sensitive, meaning that "Variable" and "variable" would be considered different identifiers. It's important to choose meaningful names for identifiers to enhance code clarity and facilitate collaboration among developers.