SaaS Definition What is SaaS? SaaS stands for at least three different "as-a-service" offerings. The original use of the acronym was to refer to Software as a Service. The term has since been used in reference to Storage as a Service and Security as a Service. Other "as-a-service" offerings include Infrastructure as a Service (IaaS) and Platform as a Service (PaaS). The combination of these two with Software as a Service is sometimes called the SPI model (for SaaS, PaaS, IaaS). The wh...