The latest Safari update features bug fixes, stability improvements, fixing some vulnerabilities in WebKit that had the potential to allow a malicious website to unexpectedly terminate an app or execute code, as well as a UI inconsistency in Safari that could allow attackers to misrepresent URLs.
You can get Safari 8.0.4 for OS X Yosemite, Safari 7.1.4 for OS X Mavericks, and Safari 6.2.4 for OS X Mountain Lion from Software Update through the Mac App Store.