North-South traffic refers to the patterns of data that travel in and out of a datacenter or between internal networks and the Internet or other remote networks. This flow is commonly observed in client-server interactions where clients are on the Internet or outside the local network. Southbound APIs and Northbound APIs are terms associated with SDN (Software-Defined Networking) and describe the interfaces that allow the SDN controller to communicate with the data plane and the application layer, respectively, and do not specifically refer to traffic flows. Core traffic is a term that might seem related, but it does not specifically correspond to the established naming of North-South or East-West traffic patterns.