Identifiers are the names you use to identify the elements in your programs. In C#, you must adhere to the following syntax rules when choosing identifiers:
You can use only letters (uppercase and lowercase), digits, and underscore characters.
An identifier must start with a letter (an underscore is considered a letter).
For example, result, _score, footballTeam, and plan9 are all valid identifiers, whereas result%, footballTeam$, and 9plan are not.