Answer Description

Infrastructure as a Service (Iaas) is a common alternative to managing a data-center or on-premise servers. With IaaS you can request virtual servers on-demand, but those servers are still your responsibility to manage from the OS level and up.

Wikipedia

Infrastructure as a service (IaaS) is a cloud computing service model by means of which computing resources are supplied by a cloud services provider. The IaaS vendor provides the storage, network, servers and virtualization (which mostly refers, in this case, to emulating computer hardware). This service enable users to free themselves from maintaining an on-premise data center. The IaaS provider is hosting these resources in either a public cloud (meaning users share the same hardware, storage, and network devices with other users), private cloud (meaning users do not share these resources), or hybrid cloud (combination of both).It provides the customer with high-level APIs used to dereference various low-level details of underlying network infrastructure like backup, data partitioning, scaling, security, physical computing resources, etc. A hypervisor, such as Xen, Oracle VirtualBox, Oracle VM, KVM, VMware ESX/ESXi, or Hyper-V runs the virtual machines as guests. Pools of hypervisors within the cloud operational system can support large numbers of virtual machines as well as the ability to scale services up and down according to customers' varying requirements.