When a program reads from a pseudo-terminal device in "cooked mode"[0], ^D is the default control character to indicate "no more input will be made available."
A program reading from a file handle other than a pseudo-terminal or a pseudo-terminal set to be in "raw mode" will behave as you describe.
A program reading from a file handle other than a pseudo-terminal or a pseudo-terminal set to be in "raw mode" will behave as you describe.
0 - https://en.wikipedia.org/wiki/Terminal_mode