Kubernetes is an extensible control loop for operating containerized computer processes distributed among multiple virtual or physical computers with a focus on highly available web applications. The desired state is typically defined in yaml or json. It offers abstractions of typically required resources and configuration like storage or network routing.
kubernetes is Open Source Software (Apache 2.0, except for some components) and owned by Linux Foundation. Using kubernetes instead of proprietary orchestration solutions from hyperscalers can prevent or mitigate vendor lock-in.