shrink-window is an interactive compiled Lisp function in `window.el'.

(shrink-window DELTA &optional HORIZONTAL)

Make the selected window DELTA lines smaller.
Interactively, if no argument is given, make the selected window
one line smaller. If optional argument HORIZONTAL is non-nil,
make selected window narrower by DELTA columns. If DELTA is
negative, enlarge selected window by -DELTA lines or columns.
Also see the `window-min-height' variable.