[1] Its most common use today is to cause a Unix terminal driver to signal end of file and thus exit programs that are awaiting input.
Unicode provides the character U+2404 ␄ SYMBOL FOR END OF TRANSMISSION for when EOT needs to be displayed graphically.
[2] In addition, U+2301 ⌁ ELECTRIC ARROW can also be used as a graphic representation of EOT; it is defined in Unicode as "symbol for End of Transmission".
The DOS Control-Z byte is actually sent and/or placed in files to indicate where the text ends.
The EOT character is used in legacy communications protocols by mainframe computer manufacturers such as IBM, Burroughs Corporation, and the BUNCH.