The build string (CFBundleVersion) is a machine-readable string required to distribute to customers and is used throughout the system to identify your app’s released or unreleased build. It’s composed of one to three period-separated integers (0-9) in the format [Major].[Minor].[Patch].
Each integer provides information about the release. For example, in 10.14.1, 10 is the major revision number, 14 is the minor revision number, and 1 is the maintenance release number.