Hybrid IT is a technique in which an enterprise uses both in-house and cloud based services to complete their entire pool of IT resources.
A hybrid IT model enables organizations to lease a portion of their required IT resources from a public/private cloud service provider. The hybrid IT approach empowers an organization by provisioning their IT resources from the cloud and gain the cost effectiveness and flexibility offered by cloud vendors while still having full control over certain resources that they might not want to expose to the cloud.
Hybrid IT is also referred to as hybrid cloud. Hybrid IT/cloud is a rapidly evolving technique, specifically in small and medium businesses, in effectively outsourcing and procuring IT resources from a cloud service provider, to cut their capital & operational costs and the management overhead required to operate an in-house infrastructure.
Though cloud services can be used to virtually procure an entire suite of IT resources, most organizations don't rely 100% on the cloud. The vast majority of organizations move certain applications to the cloud, but keep some, or even the majority, of resources in-house.