Network Policies in Kubernetes are objects that control network traffic flow within a cluster by defining which Pods can exchange network traffic. They prevent apps from communicating with each other, thus limiting the damage if one app is compromised. Each Network Policy targets a group of Pods and sets Ingress (incoming) and Egress (outgoing) network endpoints that those Pods can communicate with. These policies are additive, meaning multiple policies targeting a particular Pod apply their "allow" rules together. They represent layer 3/4 controls in the OSI networking model, providing granular options to configure network flows. However, they have limitations such as the inability to log events when a network policy block occurs and lack of support for explicit deny policies. Implementation of Network Policies depends on the CNI networking plugin used in the cluster. They are best practices for secure Kubernetes configurations, helping prevent unnecessary broadness in Pod network access.