z doesn't do anything on its own. But it pairs with a number of other things. It is used for redrawing the screen, saving and quitting, as well as manipulating folds.

Here we show z+ and how it redraws the first line out of sight at the bottom of the window to the top of the window. This is a full page down movement.

z- will redraw the cursor line to the bottom of the window.

Further Reading

:h z+ :h z-

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