Defraggler is able to analyze your drive and provide results on the current health of the drive.
This is done by analyzing the S.M.A.R.T. (Self-Monitoring, Analysis, and Reporting Technology) data to gauge its reliability and performance.
The Health tab displays S.M.A.R.T data about drive that is currently selected on the drive list.
You can find out more information on S.M.A.R.T data here!