What is Connection Tracking?
Connection tracking is what it sounds like, sort of. Keeping track of active outgoing and incoming connections being made and synchronizing that with 1 or more other systems. What this does is allow failover of, for example, a gateway to provide almost or completely lossless transition from two different servers. There's one known method I know about for Linux to allow this kind of functionality and that is through conntrackd, a feature of libnetfilter.
More to come.