Software as a Service (SaaS) means the software being used is running on servers which belong to someone else. So a key benefit of SaaS is that a user organization does not have to invest in computers and system administration to be able to use the software.
Many SaaS applications are available through any web browser. They often are priced on a pay-per-use basis. The application is usually run in the cloud, but in all cases the provider takes responsibility for server hardware and software support and maintenance.