Stands for "Java Runtime Environment" and may also be written "Java RTE." Java is a programming language, similar to C. However, since it is a newer language, it is not natively supported by all operating systems. Therefore, a Java Runtime Environment may need to be installed on your computer for Java applets and Java applications to run.
The JRE, or Java RTE, is developed by Sun Microsystems (the creator of Java) and includes the Java Virtual Machine (JVM), code libraries, and components, which are necessary to run programs written in Java. The JRE is available for multiple computer platforms, including Mac, Windows, and Unix.
If the JRE is not installed on a computer, Java programs may not be recognized by the operating system and will not run. The JRE software provides a runtime environment in which Java programs can be executed, just like software programs that have been fully compiled for the computer's processor. JRE software is available as both a standalone environment and a Web browser plug-in, which allows Java applets to be run within a Web browser.