The concept of usability put concisely is the work of years of designers attempting to describe what they are doing and within what context, in order to make the using of certain technologies and products an easier and more pleasant experience for the user.
The history of usability has been a very long endeavour, with its early roots focusing on principles of design as systemised by Roman writer Vitruvius in the 1st Century BC, who divided usability into three design principles –the strength and durability of the design (Firmitas), the relevance and suitability for the users (Utilitas) and the beauty of the design itself (Venurtas).
Ever since, the 'utilias’ principle has been used throughout various designs and products, from Leonardo Da Vinci’s Vitruvian Man that calculated the proportions of the human body, to its roots in the military, in the discipline known as Human Factors, where the question was asked what design was needed to better match soldier to weapon and also to reduce casualties. Usability meant less training was needed and precision and skills were gained.
More recently with the evolution of the digital world and computers, the concept of usability has become rather more complex. In the 1980s when computers first became popular in the home and office, most users had little or no idea of how to use the operating systems or the software. Computers seemed destined to falter before they had even begun, so it was vital that future steps be taken to increase usability.
So, what is meant by good or bad usability? It can be essentialist (such as stating that a website is not user-friendly) or it can be contextual, wherein the usability changes depending on the context, the user and the computer. In most cases, it is not so black and white, and a usability method should rely on both evaluations, based on analytics and usage data.
In order to evaluate usability, design and development teams should learn to identify the strong and the weak in a design, through inspecting the causes of bad and good usability to focusing on the features of hardware and software that are involved (such as a web browser) to interaction-focused methods, focusing on the characteristics of the user, and what user goals are determined.
Perhaps the best judge of the usability of a product such as a website, is the end user themselves. User testing sets specific goals and tasks and can provided detailed data in exposing such usability issues that may arise.
Usability is far too general a term, and there are no universal methods or rules to judge usability across all platforms and design aspects. Usability is a highly valuable design principle, and can provide solutions to many problems within the user experience, if the necessary expertise in the chosen field as well as user-centred expertise is available.