Lines of code that are added, removed, or changed from a build to another are referred to as churned. Code churn is a good measure to quantify the amount of change in your project. When you use team foundation to build your project, code coverage will calculate for you the number of lines churned. IMO, the bigger the number you get the less stable your project is; it means that you are still in the beginning and/or you have been doing a lot of changes. After a while, code churn should go down, which means that your project is more stable and this can give you a good idea about the quality of your project. Towards the end, you should get very low code churn and you should reach this stage to get higher quality as your code is much more stabilized, and accordingly, changes and bug fixes are minimal.

In Visual Studio, you can view code coverage information using the team explorer window through the Reports node.

For more info, please read: Use of Relative Code Churn Measures to Predict System Defect Density