The Java Runtime Environment (JRE) is a software package that provides the libraries, the Java Virtual Machine, and other components to run applets and applications written in the Java programming language. The JRE is part of the Java Development Kit (JDK), which contains all the necessary tools for developing Java applications.
The JRE includes the Java Virtual Machine (JVM), which is the platform that executes Java programs. It also includes the Java class libraries, which provide the functionality required by Java programs. The JRE also contains other components, such as the Java Plug-in and Java Web Start, which provide additional capabilities for running Java programs.
The JRE is available for multiple platforms, including Windows, Linux, and Mac OS. The JRE is free to download and use.