The bytecodes in Java
JVM - JVM, which stands for Java Virtual Machine, is a virtual machine that understands and runs java bytecodes.
When you compile a java program, the output is a .class file which contains bytecodes. JVM understands bytecodes and can execute the .class Java files.
There are specific implementations of the JVM for specific platforms - Windows, Linux etc. The same Java .class file can be run for any of the JVM implementations. This is how Java programming language is platform independent and make the Java programs portable i.e write once, run anywhere.
JRE - JRE, which stands for Java Runtime Environment, provides an implementation of the JVM, supporting libraries and other components required to run Java programs. JRE also provides components that enable two kinds of deployment of Java programs. Java plug-in, which enables java programs to run on browsers and Java Web Start, which deploys standalone java applications.