Software as a Service (SaaS)
Applications represent the last layer and build logically on all previous layers. Software as a Service is a business model in which the software application is no longer sold to the customer, but is made available as a service against payment.
Consequently, software and IT infrastructure are operated by an external service provider. In most cases, only an Internet-capable device and an Internet browser are required to run the software. This allows to use inexpensive hardware in the company, but at the same time to benefit from the full computer power and storage capacity of a data center.
Simply put: software is not licensed and installed on your own hardware, but is "rented" as a service and can be used anywhere with any Internet browser.