Software as Service is a category of cloud computing in which Software is

centrally hosted and it is licensed on a subscription basis. It is also known as

On-demand software. Generally, clients access the software by using a thinclient like a web browser.

Many applications like Google docs, Microsoft office etc. provide SaaS model

for their software.

The benefit of SaaS is that a client can add more users on the fly based on its

current needs. And client does not need to install or maintain any software on

its premises to use this software.

https://www.techtarget.com/searchcloudcomputing/definition/Software-as-a-Service