NetFlow is a network protocol developed by Cisco for the collection and monitoring of network traffic flow data generated by NetFlow-enabled routers and switches.
NetFlow is used by IT professionals to analyze network traffic flow and volume to determine where traffic is coming from, where it is going to, and how much traffic is being generated. NetFlow-enabled routers export traffic statistics as NetFlow records which are then collected by a NetFlow collector. The collector does that actual traffic analysis and presentation to the user and can take the form of a hardware appliance or software.
NetFlow has become a de-facto industry standard and is supported by platforms other than Cisco including; Juniper (Jflow); 3Com/HP, Dell and Netgear (sFlow); Huawei (NetStream); Alcatel-Lucent (Cflow); and Ericsson (Rflow).