BestEffort QoS is given to the Pods that do not qualify as Guaranteed or Burstable. They are Pods that consist of containers that have none of the resources defined. Containers in Pods qualified as BestEffort can use any available memory they need.

When in need of more resources, Kubernetes will start killing containers residing in the Pods with BestEffort QoS. They are the lowest priority, and they are the first to disappear when more memory is needed.