It just means that your drive is getting to the point where the manufacturer says a failure is likely. It doesn't mean you will actually have a failure, but it usually isn't a great sign either. It sounds like this is a fairly old drive, so it could be an issue.
To really test the drive, get the official drive diagnostics from whatever your HDD manufacturer is, and run that on the drive a few times on the highest detail/sensitivity level it provides. This will generally scan the entire physical structure of the drive, which is going to take quite awhile most likely, but should reveal the fault fairly simply.