per Cisco's website:
Cisco IOS NetFlow efficiently provides a key set of services for IP applications, including network traffic accounting, usage-based network billing, network planning, security, Denial of Service monitoring capabilities, and network monitoring. NetFlow provides valuable information about network users and applications, peak usage times, and traffic routing. Cisco invented NetFlow and is the leader in IP traffic flow technology.
NetFlow version 9, the latest Cisco IOS NetFlow innovation, is a flexible and extensible method to record network performance data. It is the basis of a new IETF standard. Cisco is currently working with a number of partners to provide customers with comprehensive solutions for NetFlow-based, planning, monitoring and billing.