SDN - what is orchestration
Within the realm of software defined networking, orchestration is the automated configuration, coordination, and management of computer systems and software. This can mean various things depending upon what it is applied to.
When used in the context of network orchestration which has to do with the setting up of devices, applications, and services in the network to achieve particular network objectives. The orchestrator is a single entity on the network from which the whole network infrastructure can be configured and managed as a single entity.
In other contexts, orchestration has a slightly different goal. In the context of Kubernetes for example, orchestration is focused on automating software deployment using docker images or containers.