An alphanumeric character.
"The system requires every username to consist of at least six alphanumeric characters."
of or pertaining to alphanumeric characters
"The password policy requires every code to be strictly alphanumeric, allowing only letters and numbers without any symbols."
Consisting of, or limited to, letters and/or numbers, especially the characters A to Z (lowercase and uppercase) and 0 to 9.
"The login screen only accepts an alphanumeric password that combines your chosen words with digits from zero to nine."