Thoughts on these drives...

I have two drives that through smart testing have entered "pre-fail' as a 'type' in the read out.

smartctl -H : All Drives came through as healthy

smartctl -a : Two drives have prefail in their type column, 1 with a value in #5 row

In the below image, there is a value in the #5 row which i've been told means its time to replace.

Questions:
1. Would you recommended replacing the drive in the picture that has prefail AND values in the #5 row?
2. What does pre-fail mean exactly?

Thanks,
Chris