separator character
Computing term for a character used to separate data fields or tokens, such as a comma, tab, or space.
In CSV files, commas are used as separator characters.
区切り文字 is a more common and general term for delimiter character, while 分離子文字 is a technical computing term with the same meaning.
Compound of 分離 (separation) + 子 (small element/character) + 文字 (character). A technical term likely coined in computing contexts.