Software as a Service (SaaS, typically pronounced [sæs]) is software that is deployed over the internet and/or is deployed to run behind a firewall in your local area network or personal computer. With SaaS, a provider licenses an application to customers as a service on demand, through a subscription or a “pay-as-you-go” model. Saas is also called “software on demand”. SaaS vendors develop, host, and operate software for customer use. Rather than install software on site, customers access the application over the Internet. The SaaS vendor may run all or part of the application on their hardware, or may download executable code to client machines as needed—disabling it when the customer contract expires. The software can be licensed for a single user, or group of users.
SaaS was initially widely deployed for Sales Force Automation and Customer Relationship Management (CRM). Now, it has become commonplace for many businesses tasks, including computerized billing, invoicing, human resource management, and service desk management.