alphanumeric character
Refers to characters that are either letters (英字) or digits (数字). Often used in computing and data entry contexts.
See also: 英数字
Please enter your password using alphanumeric characters.
英数字 is a more common synonym for 'alphanumeric characters', while 英数文字 explicitly includes the character (文字) aspect.
Compound of 英 (ei, 'English' or 'letter'), 数 (sū, 'number'), and 文字 (moji, 'character').