Scale bar and scale text
When one or more maps and optional grid lines, graticules and/or annotation text layers in a map window are saved as a map view, and when the map view is added to a layout, you can add a scale bar and scale text (e.g. 1 : 100000) for each map view in the layout using the layout editor.
A scale bar and a scale text largely depend on the scale that you specified to display (and print) a particular map view in the layout.
See also: