SaaS

Software as a Service delivers complete, ready-to-run applications over the internet, with the cloud provider owning every layer — physical infrastructure, operating systems, middleware, and the application itself. Customers simply authenticate and use the software; nothing is installed or patched locally. Microsoft 365 (Word, Excel, Teams, Exchange Online) is the canonical AZ-900 SaaS example. The exam distinction is the shared-responsibility boundary: in SaaS the customer is responsible only for their own data and user access. This contrasts with PaaS, where the customer still owns deployed application code, and IaaS, where the customer manages the OS and above.