Final answer:
A process is thrashing when it spends more time paging than executing, which happens when the system is overwhelmed with processes and there is insufficient memory to hold all the required pages.
Step-by-step explanation:
A process is thrashing when it is spending more time paging than executing. This occurs when the system is overwhelmed with the number of processes and the available memory is insufficient to hold all the required pages for each process. As a result, the system constantly swaps pages in and out of memory, causing a significant decrease in performance.
For example, imagine a computer with multiple running programs, and each program requires a lot of memory. However, the computer's memory capacity is limited, so the system is constantly swapping pages between the hard disk and memory, leading to a slow execution of programs.