Platform as a service (PaaS) is a category of cloud computing services that provides a platform allowing customers to develop, run, and manage applications without the complexity of building and maintaining the infrastructure typically associated with developing and launching an app. Platform as a service (PaaS) is a cloud computing model in which a third-party provider delivers hardware and software tools usually those needed for application development to users over the internet. 

IaaS. Infrastructure as a service (IaaS) is a cloud computing offering in which a vendor provides users access to computing resources such as servers, storage and networking. Instead of purchasing hardware outright, users pay for IaaS on demand. Infrastructure is scalable depending on processing and storage needs. A PaaS provider hosts the hardware and software on its own infrastructure.