SaaS
SaaS (Software as a Service) is originally referred as the Application Service Provider (ASP) model by the International Data Corporation (IDC) or it is sometimes called "on-demand software" which enables entities to access a complete business software functionality on a cloud based application.
The Software & Information Industry Association (SIIA) defines SaaS as an application or service deployed in a centralized data center across a network such as the Internet, Inranet, LAN or VPN.[1] Users maybe able to access the SaaS through subscription or by renting it from a vendor or service provider.