This document defines and describes Software as a Service (SaaS). It explains that SaaS is software deployed over the internet and accessed online rather than installed locally. Key advantages listed include accessibility from anywhere, no server maintenance requirements, scalability, and a pay-per-use pricing model. Examples provided are Gmail, Google Docs, and Salesforce. The document also discusses related concepts like Platform as a Service (PaaS), Infrastructure as a Service (IaaS), and differences between SaaS and on-premise software.