The End-of-Text character (ETX) is a control character used to inform the receiving computer that the end of a record has been reached. This may or may not be an indication that all of the data in a record have been received. It is often used in conjunction with Start of Text (STX) and Data Link Escape (DLE), e.g., to distinguish data frames in the data link layer. All this use is pretty much obsolete.
In both ASCII and EBCDIC, ETX is code point 0x03, often displayed as ^C, and a (ASCII) terminal can send it by typing Ctrl+C.
Control-C is often used to interrupt a program or process, a standard that started with Dec operating systems. In TOPS-20, it was used to gain the system's attention before logging in. mIRC uses ETX as the escape character to start a command to set the color.