IP Cameras are internet based, while CVI systems are analogue based and require cables from the recorder to the camera.
IP systems are Internet Protocol based. They are incredibly modular and flexible as they can utilise the nearest internet access point rather than needing a direct cable to the Recorder. This makes them incredibly easy to scale and extend versus a HDCVI System.
HDCVI systems are the latest platform traditional style CCTV Systems. Their protocol allows them to be retro fitted into any existing Analogue system by swapping a Recorder and the Cameras. This allows an easy upgrade to HD systems for existing systems. They also have a much lower initial cost, however the requirement of running cables will make them less flexible.
There are also hybrid systems, these allow you to mix both types. A good example of this is using CVI to replace your existing cameras, and then IP cameras in the places you wish to extend your coverage.
From a feature perspective both systems are almost identical with both the difference in cost and the flexibility of each system being the main factors in choosing whats right for a job.