Virtual Memory

Virtual Memory: 

The portion of secondary memory that execution of a program is called virtual memory.
If space needed for the program a portion of secondary memory automatically converted as a primary memory and it get backs to the secondary memory as soon as the execution of the program is finished. This is how a virtual memory works. So, this can say, virtual memory is technique for storing program or data in a secondary memory and making them appear to be in primary memory by swapping pages of segment in and out of primary memory when needed.