send-invisible
send-invisible is an interactive compiled Lisp function in `comint.el
'.
(send-invisible &optional PROMPT)
Read a string without echoing.
Then send it to the process running in the current buffer.
The string is sent using `comint-input-sender'.
Security bug: your string can still be temporarily recovered with
C-h l; `clear-this-command-keys' can fix that.