This document discusses the differences between cloud infrastructure, applications, and platforms. It notes that while cloud infrastructure provides on-demand compute and storage resources, it provides little abstraction and applications built directly on infrastructure may not scale gracefully. Cloud platforms abstract applications across cloud servers, ensure application quality of service, and provide runtime services via APIs. They provide the "glue" to allow applications to fully leverage cloud infrastructure. The document advocates for cloud application platforms over hosted platforms, as they support standard development stacks, provide portability across clouds, and essential services while cutting development costs and risks.