Noun
stdin (uncountable)
(computing) Standard input: a stream mapped to the primary input device, typically a keyboard.
Launching NT processes from within bash is great, but in order to support NT command-line utilities there needs to be a way for NT binaries to access the file descriptors that represent stdin, stdout, and stderr inside a WSL process. Source: Internet
It sends messages to the process via its stdin and receives messages from the process via its stdout. Source: Internet