Alphanumericals or alphanumeric characters are any collection of number characters and letters in a certain language. Sometimes such characters may be mistaken one for the other.
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 and 0–9, case insensitive) or 62 (A–Z, a–z and 0–9, case-sensitive) alphanumeric characters.