In computer data, a substitute character (␚) is a control character that is used to pad transmitted data in order to send it in blocks of fixed size, or to stand in place of a character that is recognized to be invalid, erroneous or unrepresentable on a given device. It is also used as an escape sequence in some programming languages.
In the ASCII character set, this character is encoded by the number 26 (1A hex). Standard keyboards transmit this code when the Ctrl and Z keys are pressed simultaneously (Ctrl+Z, often documented by convention as ^Z).[1] Unicode inherits this character from ASCII, but recommends that the replacement character (�, U+FFFD) be used instead to represent un-decodable inputs, when the output encoding is compatible with it.