What is "S.M.A.R.T." or "smartd" ?

Question

What is the service "S.M.A.R.T." or "smartd"?

Answer

smartd is a daemon that monitors the Self-Monitoring, Analysis, and Reporting Technology (S.M.A.R.T) system built into many types of hard drives. The self-monitoring system is the way a Hard Drive measures its reliability to see if it is failing. 

For more information, can be found here: 

https://linux.die.net/man/8/smartd