Apple today released an updated and revised version of iTunes 12.6.1, which was originally releasedalongside the macOS Sierra 10.12.5 update on Monday, May 15. 

The new version of iTunes is 12.6.1.27, while the previous version was 12.6.1.25. It's not clear why Apple has released a new minor update to iTunes 12.6.1, but it presumably includes some unspecified bug fix. 

According to the release notes, the update "includes minor app and performance improvements." These are the same generic release notes that were included in the first iTunes 12.6.1 release. 

The new version of iTunes 12.6.1 can be downloaded for free using the Software Update function in the App Store.

Source: macrumors