Today Apple released OS X 10.10.5, the 5th major update for OS X 10.10 Yosemite. This update doesn’t add any new features, but takes care of several bugs and provides other minor fixes for OS Yosemite. It is recommended that everyone running OS Yosemite updates as soon as possible.
You can update your system by going to the Apple menu, choosing App Store, and switching to the Updates tab.
Also released were security updates for OS X 10.9 Mavericks and OS X 10.8 Mountain Lion. Updates for those systems can by found by clicking the Apple menu, then Software Update.
This is likely the last major update for OS X Yosemite, with OS X 10.11 El Capitan coming out soon. My personal uninformed prediction is we will see El Capitan in late October.