Technical term used in computing to refer to a set of characters consisting of letters and digits.
Only alphanumeric character sets can be used for the password.
英数字 refers to alphanumeric characters in general, while 英数字集合 specifically denotes a set or collection of such characters, often in a technical context.
alphanumeric character set
Compound of 英数字 (alphanumeric characters) and 集合 (set). The exact historical derivation is uncertain; the term is a modern technical coinage.