Infrastructure as a Service (IaaS) is a type of cloud computing service that provides virtualized computing resources over the internet. IaaS providers offer customers access to virtualized computing resources, such as virtual machines, storage, and networking, that can be used to run applications and store data. Examples of IaaS providers include Amazon Web Services (AWS), Microsoft Azure, and Google Cloud Platform.

Platform as a Service (PaaS) is a type of cloud computing service that provides a platform for customers to develop, run, and manage applications without the complexity of building and maintaining the underlying infrastructure. PaaS providers offer customers a platform, including a development environment, runtime environment, and data storage, that can be used to build and deploy applications. Examples of PaaS providers include Heroku, AWS Elastic Beanstalk, and Google App Engine.

In summary, IaaS is lower level in the stack, it provides the infrastructure such as servers, storage, and networking, while PaaS is higher level in the stack, it provides a platform for customers to develop, run and manage their applications.