Platform as a Service (PaaS) is a cloud model where the provider operates much of the platform layer: servers, operating system, middleware, runtime, patching, and scaling. The customer focuses on the application, its configuration, identities, secrets, and the data it processes. This reduces infrastructure work, but it does not remove security responsibility.
PaaS matters because attackers often target the parts the customer still controls. Weak access policies, exposed API keys, insecure code, misconfigured storage, or poor logging can lead to data theft or code abuse even when the platform is fully managed. Defenders use PaaS to reduce patching burden and speed delivery, but they still need least privilege, secure secret storage, input validation, and audit logging. In practice, PaaS security is about understanding the boundary: the provider secures the service, while the customer secures what runs on it and what it stores.