Java Runtime Environment
Java Runtime Environment is a part of the Java platform. The Java platform refers to a group of software products from Oracle. The platform is used to develop and run Java programs. The platform includes the execution engine (called a Java Virtual Machine) that allows the same Java programs to run on different computer systems.
Pure Java applications have a big advantage. They can run on any operating system without the need for developers to prepare a binary package or a installer for each operating system. On the other hand Java applications do require a "Java Runtime Environment" (JRE), and this installation does depend on the operating system you are running. This page explains how to install JRE on your machine and how to run a Java application though the Java runtime.
Much software in the OSM ecosystem depends on the Java Runtime Environment:
How to install
Main article: Java Runtime Environment/How to install
How to run a Java application
Main article: Java Runtime Environment/How to run java applications