function character
Technical computing term for a character that performs a control function rather than representing printable data, such as a newline or tab.
Newlines and tabs are types of function characters.
制御文字 (control character) is a near-synonym often used interchangeably, but 機能文字 may be preferred in certain standards or contexts.
Compound of 機能 (function) and 文字 (character), likely a calque from English 'function character'.