JVM stands for Java Virtual Machine which is also known as run-time engine that is the reason behind platform independence ability of java (both hardware and software).  A java program can be considered like compiled as well as interpreted (Write Once and Run Anywhere). 

The source code file of java program will be saved with .java extension.  The compiled java program creates a java byte code file with .class extension.  The byte code is handled by JVM of the platform on which program is executing.  The JVM translates the byte code into such a language that can be understandable by the machine based on its platform (operating system or configuration).

VM Vs JDK Vs JRE

JDK stands for Java Development Kit that contains everything needed to develop java program along JRE.

JRE is also known as Java Runtime Environment consists of JVM, class libraries, compiler, debugger and other files required to run java program.

Using JRE you can run java program but not develop it.

JVM or Java Virtual Machine is component of JRE and handles the bytecode and enable us to run java program on a particular platform.