An IP Camera is a security camera which allows you to view live, full motion video from anywhere in the world. IP Cameras can be used for surveillance of both homes and businesses.
A hidden camera is a security camera for filming people without their knowledge. The security camera is "hidden" because it is either not visible to the subject, or is disguised as another object.
A CCTV camera is a high resolution security camera. CCTV system is a general term used for a complete security system including security camera, monitor, time lapse VCR etc.