Basically it means that your disk/drive is due for a routine error check. Think of it like taking your car in to be given a quick once over every couple thousand miles. Most of the time, nothing's wrong, it takes a fairly short period of time, and you're done. However, sometimes something is found to be wrong, and it's generally better to head it off before it becomes a big problem.
What does the computer message: "one of disks needs to be checked for consistency" mean?