A CV is a specialized type of résumé that is generally used in the education and health related fields. It differs from the resume in that it is much more detailed; running more than two pages in length, and provides specific, comprehensive information about the person's career and education.
In the CV all of the educational background of the person is listed including the titles of the Master's thesis and doctoral dissertations, honors and awards and other accolades. For the undergraduate-courses that pertain to the field or the job you are seeking should be listed. There is also a complete list of work experience, all publications that the person has authored, coauthored or collaborated on, a list of all conference presentations and all professional memberships.
As you can see, a CV is generally best used for midcareer changers who have had a lot of experience in their field.