Release notes describe how the software has changed in a particular build, and the issues known to exist in that build.
The release notes document includes all or some of the following sections:
What's New: The enhancements and other changes released in the build.
Fixed Issues: The issues that are fixed in the build.
Known Issues: The issues that exist in the build.
Points to Note: The important aspects to keep in mind while using the build.
Limitations: The limitations that exist in the build.
For the latest release notes (build 57.11), click this link.