"Hybrid cloud is a cloud computing environment which uses a mix of on-premises, private cloud and third-party, public cloud services with orchestration between the two platforms. Many established businesses have physical data centers around the world and are in the process of migrating applications and workloads to the cloud. This is a massive effort and can’t be done all at once. Some applications continue to live on-premise while others live in the cloud to minimize risk and manage costs. Because applications are running in multiple cloud environments, they need to be able to interoperate with each other, which is why many of the cloud providers today provide services like VPN Gateways which allow you to directly connect your cloud to your on-premise data center, and operate both systems as if it was a single cloud."
in other words
It's like the Prius. You get the best of a gas and electric car without fully committing to either.