The capability provided to the consumer is 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 networks, servers, operating systems, or storage, but has control over the deployed applications and possibly configuration settings for the application-hosting environment.
Platform-as-a-Service (PaaS) is a model of service delivery whereby the computing platform is provided as an on-demand service upon which applications can be developed and deployed. Its main purpose is to reduce the cost and omplexity of buying, housing, and managing the underlying hardware and software components of the platform, including any needed program and database development tools. The development environment is typically special purpose, determined by the cloud provider and tailored to the design and architecture of its platform. The cloud consumer has control over applications and application environment settings of the latform. Security provisions are split between the cloud provider and the cloud consumer.
The following answers are incorrect: Software-as-a-Service.
Software-as-a-Service (SaaS) is a model of service delivery whereby one or more applications and the computational resources to run them are provided for use on demand as a turnkey service. Its main purpose is to reduce the total cost of hardware and software development, maintenance, and operations. Security provisions are carried out mainly by the cloud provider. The cloud consumer does not manage or control the underlying cloud infrastructure or individual applications, except for preference selections and limited administrative application settings.
Infrastructure-as-a-Service. Infrastructure-as-a-Service (IaaS) is a model of service delivery whereby the basic computing infrastructure of servers, software, and network equipment is provided as an on-demand service upon which a platform to develop and execute applications can be established. Its main purpose is to avoid purchasing, housing, and managing the basic hardware and software infrastructure components, and instead obtain those resources as virtualized objects controllable via a service interface. The cloud consumer generally has broad freedom to choose the operating system and development environment to be hosted. Security provisions beyond the basic infrastructure are carried out mainly by the cloud consumer Code as a Service (CaaS) CaaS does not exist and is only a detractor. This is no such service model.

Cloud Deployment Models
NOTE: WHAT IS A CLOUD INFRASTRUCTURE? A cloud infrastructure is the collection of hardware and software that enables the five essential characteristics of cloud computing. The cloud infrastructure can be viewed as containing both a physical layer and an abstraction layer. The physical layer consists of the hardware resources that are necessary to support the cloud services being provided, and typically includes server, storage and network components. The abstraction layer consists of the software deployed across the physical layer, which manifests the essential cloud characteristics. Conceptually the abstraction layer sits above the physical layer.
The following reference(s) were/was used to create this question: NIST Special Publication 800-144 Guidelines on Security and Privacy in Public Cloud Computing and NIST Special Publication 800-145 The NIST definition of Cloud Computing