Alphanumeric characters, also referred to as alphameric characters, are the set of alphabetical letters and numerical characters in a language. The alphanumeric characters for the English language include the 26 alphabetical letters (A - Z) along with the 10 numerical characters (0 - 9). In some cases, the set of alphanumeric characters include both uppercase and lowercase letters. Languages other than English may include letter variations, such as é and ç.
Non-alphanumeric characters are all characters other than alphabetical letters and numerical characters. These can include punctuation characters like commas (,), question marks (?), colons (:), and exclamation marks (!), as well as special characters like equal symbols (=) and apostrophes (‘).
A programming language is a formal set of rules along with a unique syntax for instructing a computer to perform tasks.
A username (or user name, user ID, or account name) is a name that uniquely identifies a user in a system.