In computer programming language, identifiers are the names used by users in programming, which are used to name variables, constants, functions, sentence blocks and so on. To establish the relationship between name and usage. Identifiers usually consist of letters, numbers and other characters.
Identifiers are divided into system-defined identifiers and user-defined identifiers. System-defined identifiers refer to identifiers with fixed names and specific meanings, which are divided into keywords and predefined identifiers. User-defined identifiers are used to name operational objects, such as variables, arrays and functions used by users.