In the C0 control code set used in ASCII, ETB is a short name for the End-of-Transmission-Block character (code 23, or 0x17, or ^W in caret notation). It is a communication control character used to indicate the end of a block of data for communications purposes. ETB is used for blocking data when the block structure is not necessarily related to the processing function.
References
End-of-Transmission-Block character Wikipedia(Text) CC BY-SA