Infrastructure as a Service (IaaS) is a cloud service model that provides virtual servers, storage, networking, and other infrastructure over the internet. You manage the operating system, applications, and data, while the cloud provider manages the physical hardware.
For example, you can launch an Amazon EC2 virtual server on AWS instead of buying a physical server. You can install software, configure the server, and pay only for the resources you use.
In simple words, IaaS gives you cloud infrastructure without the cost and maintenance of physical hardware.