Ultrabook +
Ultrabook is a marketing term, originated and trademarked by Intel, for a category of high-end laptop computers.
They were originally marketed as featuring ultra thin form factor and light weight design without compromising battery life or performance, and when the term was originated they generally were enough smaller than average laptop models to qualify as subnotebooks.
As ultrabook features became more mainstream in the mid-late 2010s, explicitly branding laptop models as ultrabooks became much less frequent. As of 2021, while Intel maintains the Ultrabook trademark, it is rarely used for new models and has been superseded in Intel's own marketing by the Intel Evo branding. The term "ultrabook" has since become a generic trademark.