Infrastructure as a Service (IaaS) describes a delivery model of cloud computing services which gives system administrators access to cloud-hosted virtual computers and system primitives used to architect and operate hosted software systems.
The National Institute of Standards and Technology (NIST) defined infrastructure as a service (IaaS) in its 2011 definition of cloud computing:
The capability provided to the consumer is to provision processing, storage, networks, and other fundamental computing resources where the consumer is able to deploy and run arbitrary software, which can include operating systems and applications. The consumer does not manage or control the underlying cloud infrastructure but has control over operating systems, storage, and deployed applications, and possibly limited control of select networking components such (ex. host firewalls).