

Today's beta, build number 14F19a, can be downloaded through the Software Update mechanism in the Mac App Store or through the Apple Developer Center.
The first OS X 10.10.5 beta did not appear to include any consumer-facing changes, so it's likely that this update focuses on behind-the-scenes bug fixes and performance enhancements.
Over the course of its lifespan, OS X Yosemite has received four updates. The first two brought bug fixes and security improvements, while OS X 10.10.3, the most significant update to Yosemite, introduced the new Photos app, Force Touch APIs, new emoji features, and more.
OS X 10.10.4, the current version of Yosemite, also focused on bug fixes and stability improvements, most notably introducing TRIM support for third-party SSDs and eliminating the Discoveryd process that caused ongoing connectivity issues in the OS.
Article Link: Apple Seeds Second OS X 10.10.5 Yosemite Beta to Developers