Difference between the "Bundle versions string, short" and the "Bundle version"

"Bundle versions string, short" is the version we see it in the App Store, e.g. 1.0.1

"Bundle Version" is the build number, e.g. 12

When you want to submit a new APP but do not want to change the version number, you would just update the build number, with same version string

And build number can/should be start over for every version string

For example, we could have these version and build:

Version:1.0.1 Build:1 Version:1.0.1 Build:2 Version:1.0.1 Build:3

Version:1.0.2 Build:1 Version:1.0.2 Build:2 Version:1.0.2 Build:3 Version:1.0.2 Build:4

Here is a good article if you want to understand all the concepts about this version thing: https://developer.apple.com/library/ios/technotes/tn2420/_index.html