Value: The current, normalized value of the attribute. Higher values are always better (except for temperature for hard disks of some manufacturers). The range is normally 0-100, for some attributes 0-255 (so that 100 resp. 255 is best, 0 is worst). There is no standard on how manufacturers convert their raw value to this normalized one: when the normalized value approaches threshold, it can do linearily, exponentially, logarithmically or any other way, meaning that a doubled normalized value does not necessarily mean “twice as good”.
Worst: The worst (normalized) value that this attribute had at any point of time where SMART was enabled. There seems to be no mechanism to reset current SMART attribute values, but this still makes sense as some SMART attributes, for some manufacturers, fluctuate over time so that keeping the worst one ever is meaningful.
Threshold: The threshold below which the normalized value will be considered “exceeding specifications”. If the attribute type is “Pre-fail”, this means that SMART thinks the hard disk is just before failure. This will “trigger” SMART: setting it from “SMART test passed” to “SMART impending failure” or similar status.
Type: The type of the attribute. Either “Pre-fail” for attributes that are said to indicate impending failure, or “Old_age” for attributes that just indicate wear and tear. Note that one and the same attribute can be classified as “Pre-fail” by one manufacturer or for one model and as “Old_age” by another or for another model. This is the case for example for attribute Seek_Error_Rate (ID 7), which is a widespread phenomenon on many disks and not considered critical by some manufacturers, but Seagate has it as “Pre-fail”.
Raw value: The current raw value that was converted to the normalized value above. smartctl shows all as decimal values, but some attribute values of some manufacturers cannot be reasonably interpreted that way (for the details: Wikipedia: S.M.A.R.T.: Known ATA S.M.A.R.T. attributes).
