noun
Computing term for characters beyond standard letters and digits, such as @, #, $, %, &, *, etc.
パスワードには特殊文字を含めてください。
Please include a special character in your password.
記号 is a broader term for symbols and marks, while 特殊文字 specifically refers to non-alphanumeric characters in computing contexts.
Compound of 特殊 (special) and 文字 (character).