Software as a service (SaaS) allows users to connect to and use cloud-based apps over the Internet. Common examples are email, calendaring, and office tools (such as Microsoft Office 365) SaaS provides a complete software solution that you purchase on a pay-as-you-go basis from a cloud service provider. All of the underlying infrastructure, middleware, app software, and app data are located in the service providers data center. The service provider manages the hardware and software and will ensure the availability and the security of the app and your data.”]
Source: https://azure.microsoft.com/en-us/overview/what-is-saas/