meaning

Best explanation I can find is from the following Version Comaptibilty T/N:

http://www.symantec.com/business/support/index?page=content&id=TECH29677

• A major release is the first in a series of single-dot releases such as 2.0 or 7.0. This type of release contains new features, new supported platforms, and a complete set of the latest product documentation. These releases are available from FileConnect.
• A minor release is a single-dot release that follows a major release, for example, 2.1, 7.1, 7.5, and so forth. This release type contains much of the same requirements as a major release. It contains a smaller set of new features and enhancements, platform proliferations, and a complete set of updated documentation. These releases are available from FileConnect.
• A release update is a double-dot release, for example, 2.0.1, 7.0.1, 7.0.2, and so forth. This release type may contain a few new features and enhancements as well as a many product fixes. Only those documents that are applicable to the new features or enhancements are updated and republished. These releases are available on the Support website and are listed below.
• A maintenance update is a triple-dot release, for example, 2.0.0.1, 7.1.0.1, 7.1.0.2, and so forth. This release type is comprised of a small number of fixes that are developed to address issues in either a major, minor, or release update. This release type only contains fixes to known issues and does not contain new features or enhancements to NetBackup.

So the answer to your question "What is the meaning of NBU 7.1.0.2" --> NetBackup 7.1 Maintenance Release 2 as stated by Jackie007