non-jōyō kanji; kanji outside the common-use list
Refers to kanji not included in the 常用漢字 (jōyō kanji) list. Often used in discussions of Japanese orthography and education.
Non-jōyō kanji include characters that are often seen in newspapers.
The official list of commonly used kanji; 表外字 are those not on this list.
Compound of 表 (hyō, 'table, list') + 外 (gai, 'outside') + 字 (ji, 'character'), referring to characters outside the official list.