noun
character number
Computing term for a numeric code assigned to a character, such as in character encoding.
各文字には固有の文字番号が割り当てられている。
Each character is assigned a unique character number.
文字コード is a more common term for character encoding, while 文字番号 specifically refers to the numeric identifier of a character within an encoding scheme.
Compound of 文字 (character) and 番号 (number).