Understanding the Layout Process in Qt Widgets (felipefarinon.com)
UI frameworks are code libraries that provide input management, UI widgets and rendering APIs for application developers. Along the lifecycle of a UI, these widgets have to be shown and arranged on the screen according to the intentions of the developers, and frameworks have evolved some mechanisms for describing this arrangement in an abstract way. Once the descriptions are in place, the toolkit becomes responsible for positioning and resizing the elements. This is what we call layout management.