A page fault occurs when a program requests an address on a page that is not in the current set of memory resident pages.
The below blog is for the the Basics of Page Faults
As I'm not aware of what technology used to build your app (.Net/Java), here is the below link which can help you to understand on the out of memory/memory leak causes for Java app.
Also, below links helps you to drill down on the memory leaks, if you app is java or .Net. Certain amount of physical memory is allocated out of the server memory to the app server, it is called Heap memory - if application is not able to find any free space from the heap for allocating the objects further it throws the out of memory error, so in this case we need to analyse why this issue is occurring and need to take actions like increasing the heap space(which is not recommended always), finding out the object(collections, static objects etc.,) which is causing the memory leaks through the below analysis.