There is nothing particularly special about "-", but a lot of programs do use it for standard input like you said. e.g. awk, cat, diff. My macOS system has a

There is nothing particularly special about "-", but a lot of programs do use it for standard input like you said. e.g. awk, cat, diff. My macOS system has a quite a few of these grep -e '-.*standard input' /usr/share/man/man1/*