A page fault is an interruption that occurs when a software program attempts to access a memory block not currently stored in the system's RAM. This exception tells the operating system to find the block in virtual memory so it can be sent from a device's storage (SSD or HD) to RAM.
While most page faults are normal background processes in Windows, macOS, and Ubuntu, some are invalid and can cause issues. An invalid page fault is when a program tries to access a memory address that doesn't exist. If the program cannot find a new address, the operating system may terminate that program, resulting in a crash.