Safari for Mac
Safari is included with your Mac operating system.
Before reinstalling, you might want to use Spotlight to search for Safari on your Mac. If you find it, but it's no longer in your Dock, just drag it to the Dock to add it back.
Safari for Windows
Apple no longer offers Safari updates for Windows. Safari 5.1.7 for Windows was the last version made for Windows, and it is now outdated.