In a "logical pixel" system (macOS, Wayland, …Android??) the scale is the relationship between logical and physical pixels. In an "app go draw bigger stuff" system like Windows, it's just the factor of how much bigger the UI elements should be. E.g. in Windows settings you can set 150% scale and all UI elements will be 1.5X as large.
And the "good" scale depends mostly on PPI of the monitor, as well as user preference. On a 27" 4K monitor, 1x scale is near unusable: the UI elements would be microscopic. Windows defaults to 150%, but 175% and 200% are fine as well (here's the user preference aspect).
