Define Demand Paging, Page fault interrupt, and Trashing?

Demand Paging: Demand paging is the paging policy that a page is not read into memory until it is requested, that is, until there is a page fault on the page.

Page fault interrupt: A page fault interrupt occurs when a memory reference is made to a page that is not in memory.

The present bit in the page table entry will be found to be off by the virtual memory hardware and it will signal an interrupt.

           Trashing: The problem of many page faults occurring in a short time, called “page                 thrashing,”