JAVA_HOME is an operating system (OS) environment variable which can optionally be set after either the Java Development Kit (JDK) or the Java Runtime Environment (JRE) is installed.

After you install Java and the JDK on Ubuntu, it's customary to set the JAVA_HOME environment variable as well. To do this, simply edit the user's environment configuration with the following command: ...

A PATH variable stores directory shortcuts. Learn How to add, modify or edit a PATH Environment Variable in Windows 11/10.

If you want to download and install Java JDK 18 on Windows 11/10 computer, you will also have to set up a Path in Environment Variable.