Java has been in the news a lot lately. Not good news, either. What is Java? Well, its a very universal computing platform that is used by many apps and some websites. It no longer comes on new Macs, you have to download it manually when your Mac first encounters an app or website that requires it.
So the news is that Java has some security holes in it. That has been true for some time now, but recently new holes have been discovered. However, Java actually has a couple of different forms on your Mac. There is Java that works with apps and then there is Java that runs in your web browser (as a plug-in). It is the latter that has the recently discovered security holes.
Now, next time you use Safari Java will be disabled. If you run into a site that needs it, it will tell you and you can temporarily re-enable it with the steps above.
If you do not use Safari, well, I wonder why not. Safari has changed a lot recently and I find it to be superior to other browsers available for your Mac. Additionally, iCloud syncs your Safari Bookmarks with your iPad and iPhone automatically. Other browsers cannot do this. So, if you are using Firefox or Chrome or any other browsers, give the new Safari a try!