What actually is cloud computing?
In cloud computing, there are generally three so-called cloud service levels (CSE) that build on one another: Infrastructure as a Service (IaaS), Platform as a Service (PaaS) and Software as a Service (SaaS). What all three levels have in common is that abstracted or virtualized IT infrastructures are made available. It follows that IaaS, PaaS and SaaS, like all cloud computing services, can be dynamically adapted to the needs of users or companies at any time.

Source: https://www.global.de/blog/iaas-paas-saas/