One of the biggest challenges for software programmers is incompatible operating systems. A program they write for PC isn't going to work on a Mac or a Blu-ray player.
I'm sure you've run into this kind of thing before. An app that's great on Androids doesn't work on iOS systems or vice versa.
That's why some software is designed for programmers to write one program and run it on any system. The most widespread of these cross-platform systems is Java.
Thanks to the rise of cross-platform Web browsers and cloud computing, Java isn't as important as it once was. Still, without it certain websites, online games and even useful programs like LibreOffice won't run.
And you can't ignore that it's installed on an estimated 3 billion gadgets - including most new PCs you buy. Macs no longer have it installed by default.
Unfortunately, hackers have had a good few years picking apart Java for its security flaws. Important: if you're running an older, out of date version of Java, your computer is in serious danger.