What is Alphanumeric ?

 A string of characters containing both letters (A-Z) and numbers (0-9).

An alphanumeric text entry field will accept both letters and numbers. An alphanumeric keypad is one with both letters and numbers on the keys.

Alphanumericals are a combination of alphabetical and numerical characters, and is used to describe the collection of Latin letters and Arabic digits or a text constructed from this collection.

Merriam-Webster suggests that the term "alphanumeric" may often additionally refer to other symbols, such as punctuation and mathematical symbols.

In the POSIX/C locale, there are either 36 (A-Z+0-9, case insensitive) or 62 (A-Z+a-z+0-9, case-sensitive) alphanumeric characters.

In some usages, the alphanumeric character set may include both upper- and lower-case letters, punctuation marks and symbols -- such as @, &, and *. For languages other than English, alphanumeric characters include letter variations with accents, such as é and ç.