The talk was about control theory and the reconciliation pattern in Kubernetes. The speaker explained the basic principles of control theory and how it is used to bring a system into a desired state. They also discussed the use of the reconciliation pattern in Kubernetes and how it is implemented in Cluster API. They showed a demo of how the reconciliation pattern is used to update a cluster's version in real time. The talk provided an overview of control theory and its application in Kubernetes, specifically in the Cluster API.