In programming languages like Java, keywords are reserved words with predefined functionality. They cannot be used as identifiers (variable names, class names, etc.) because they have a specific purpose within the language.
Related terms
reserved word: A reserved word is a term used interchangeably with keyword. It refers to words that have predefined meanings in programming languages.
identifier: An identifier is a name given to entities such as variables, methods, classes, etc., in programming. Unlike keywords, identifiers are user-defined and should not clash with reserved words.
syntax: Syntax refers to the set of rules that define how code should be written in order for it to be considered valid by the programming language's compiler or interpreter.