What Is The Java Runtime Environment

At first glance, the Java Runtime Environment (JRE) appears to be a straightforward piece of infrastructure: a software package that lets you run Java programs. But this description is like saying a particle accelerator "lets you see atoms." It is technically true, but it misses the radical, almost philosophical, nature of the artifact.

But what exactly is it? And why do you need it to run Java applications but not applications written in languages like C++ or Python? what is the java runtime environment