JVM is short for Java Virtual Machine. JVM is an abstract computing machine, or virtual machine. It is a platform-independent execution environment that converts Java bytecode into machine language and executes it. Most programming languages compile source code directly into machine code that is designed to run on a specific microprocessor architecture or operating system, such as Windows or UNIX.
Recommended Reading: Webopedia Study Guides – Java Basics: Variables, Syntax and Conventions and Java Basics Part 2: Operators, Modifiers and Structures.
A Machine Within a Machine
JVM — a machine within a machine — mimics a real Java processor, enabling Java bytecode to be executed as actions or operating system calls on any processor regardless of the operating system. For example, establishing a socket connection from a workstation to a remote machine involves an operating system call. Since different operating systems handle sockets in different ways, the JVM translates the programming code so that the two machines that may be on different platforms are able to connect.
JVMs are not the only virtual machines being used today.