noun, noun which may take the genitive case particle 'no'
multicharacter; multiple characters
Computing term used to describe strings, patterns, or inputs consisting of more than one character.
パスワードは複数文字で入力してください。
Please enter a password with multiple characters.
この検索機能は複数文字のパターンに対応している。
This search function supports multicharacter patterns.
文字列 means 'character string' and is more common in general computing contexts. 複数文字 specifically emphasizes the presence of multiple characters, often in contrast to a single character.
Compound of 複数 (multiple) and 文字 (character). A straightforward modern technical term.