An Operator is a method of packaging, deploying and managing a Kubernetes application. A Kubernetes application is an application that is both deployed on Kubernetes and managed using the Kubernetes APIs and kubectl tooling. To be able to make the most of Kubernetes, you need a set of cohesive APIs to extend in order to service and manage your applications that run on Kubernetes. You can think of Operators as the runtime that manages this type of application on Kubernetes.
The principal purpose of the Operator Framework SIG is to discuss, develop and disseminate best practices for building Operators, using Operators and help grow the Operator ecosystem by engaging and learning from Operator authors, users and contributors to the Operator Framework itself.