In context of networking I keep running into statements such as "east-west traffic is larger than north-south traffic". I have tried a bit of googling but have not been able to locate an authoritative answer to understand the origin of these terms.


What is the definition of north-south traffic?
What is the definition of east-west traffic? 
What is the origin of these terms? 


The terms are usually used in the context of data centers.

Generally speaking, "east-west" traffic refers to traffic within a data center -- i.e. server to server traffic.  "North-south" traffic is client to server traffic, between the data center and the rest of the network (anything outside the data center).

I believe the terms have come into use from the way network diagrams are typically drawn, with servers or access switches spread out horizontally, and external connections at the top or bottom.
