It's been nearly three years since the NIST (National Institute of Standards and Technology) published what has become the standard definition of cloud computing. Both the tech industry and IT organizations have been good about following the NIST definitions for IaaS and SaaS -- not so much for PaaS, a terms that remains confusing and is used confusingly.
The NIST definition (PDF) of PaaS still stands, as far as I'm concerned:
Platform as a Service (PaaS): The capability provided to the consumer to deploy onto the cloud infrastructure consumer-created or acquired applications created using programming languages, libraries, services, and tools supported by the provider. The consumer does not manage or control the underlying cloud infrastructure, including network, servers, operating systems, or storage, but [it does have] control over the deployed applications and possibly configuration settings for the application-hosting environment.
InfoWorld/ full read here/ http://www.infoworld.com/d/cloud-computing/what-does-paas-really-mean-let-us-know-if-you-find-out-244807