Usability is a quality attribute that assesses how easy user interfaces are to use. — Jakob Nielsen —Usability 101: The What, Why and How of User-Centered Design (Alert Box)
Huh? Quality attribute? Maybe that’s an important and useful technical term in information design, but I wouldn’t put it in a 101 course. How about (the admittedly simplistic) “Usability is the measure of how easy things are to use.”
Nielsen appears to be re-trenching; the internal links in his document point to meaty sites on the NNGroup (a research team that sells reports) — he seems to be calling attention to work done by his associates. Jakob is possibly hoping that more people will use this “101” page as an entry point to usability studies, rather than some of his older classic works (the ones that contributed to his near-cult status).