A measure of how effectively visitors are able to use a website. Usability is important in the marketing of the website and the services that it provides: 80% of website visitors abandon commercial websites before they make a purchase. Nielsen's Law of the Internet is that ‘users spend most of their time on other people's websites’. It is vital in an age of low tolerance to delay and short attention spans to increase a website's stickiness, to encourage multiple click-through, and create higher conversion rates. Ease of use is a prerequisite to all of these.