https://www.oracle.com/cloud/what-is-iaas/
What Is IaaS?
Infrastructure as a service (IaaS) is a type of cloud service model in which computing resources are hosted in the cloud. Businesses can use the IaaS model to shift some or all of their use of on-premises or colocated data center infrastructure to the cloud, where it is owned and managed by a cloud provider. These infrastructure elements can include compute, network, and storage hardware as well as other components and software.
In the IaaS model, the cloud provider owns and operates the hardware and software and also owns or leases the data center. When you have an IaaS solution, you rent the resources like compute or storage, provision them when needed, and pay for the resources your organization consumes. For some resources such as compute, you'll pay for the resources you use. For others such as storage, you'll pay for capacity.
How Does IaaS Work?
In a typical IaaS model, a business-which can be of any size-consumes services like compute, storage, and databases from a cloud provider. The cloud provider offers those services by hosting hardware and software in the cloud. The business will no longer need to purchase and manage its own equipment, or space to host the equipment, and the cost will shift to a pay-as-you-go model. When the business needs less, it pays for less. And when it grows, it can provision additional computing resources and other technologies in minutes.
In contrast, in a traditional on-premises scenario, a business manages and maintains its own data center. The business must invest in servers, storage, software, and other technologies, and hire an IT staff or contractors to purchase, manage, and upgrade all the equipment and licenses. The data center has to be built to meet peak demand, even though sometimes workloads decline and those resources stand idle. Conversely, if the business grows quickly, the IT department might struggle to keep up.