Cloud services consist of 3 main models: IaaS (Infrastructure-as-a-Service), PaaS (Platform-as-a-Service) and SaaS (Software-as-a-Service).
IaaS (Infrastructure-as-a-Service)
It is a server/database which is managed by the cloud provider. It is possible to create an application on IaaS instead of managing the backend of our applications ourselves.
PaaS (Platform-as-a-Service)
PaaS allows you to go further than IaaS because it provides development tools as well as an infrastructure and multiple supports to design applications.
SaaS (Software-as-a-Service)
A completely built cloud application.