SaaS is also called hosted software or on-demand software.
SaaS is the natural evolution of software. For many years, the old mode of obtaining physical DVD and installing it on the local server was the only feasible solution. In fact, many scenarios still need client-server mode. In other words, in recent years, many developments have made SaaS mainstream. One factor is that bandwidth and internet are much faster than ten years ago. Other major factors include the virtualization of big data and the development of tools. All these advances make it easier for providers to expand and manage their own infrastructure to provide SaaS solutions.
SaaS is used in many common business fields, including customer relationship management (CRM), document management, accounting, human resources (HR) management, service desk management, content management and collaboration. There are thousands of SaaS providers, but Salesforce.com is probably the most famous example, because it is one of the first providers to break the vertical market of traditional software.