Good question; I don't have single definition for "operating system". The Wikipedia page for Operating Systems says "An operating system (OS) is software that

Good question; I don't have single definition for "operating system". The Wikipedia page for Operating Systems says "An operating system (OS) is software that manages computer hardware and software resources and provides common services for computer programs", and by that definition, the JVM would count as one. Though most users also expect some GUI/Desktop from an OS, and that's what browsers offer, but not the JVM. (The JVM allows programs to have a GUI, but it doesn't have a GUI itself, for example for launching other programs).