What are the rules for valid identifiers?

Valid identifiers in programming must start with a letter (a-z, A-Z) or an underscore (_), followed by letters, digits (0-9), or underscores. They cannot contain spaces or special characters like punctuation marks. Identifiers are case-sensitive and should not be a reserved keyWord in the programming language being used. Additionally, it's best practice to choose meaningful names that convey the purpose of the identifier.