Original: Self-Monitoring, Analysis, and Reporting Technology, or S.M.A.R.T. (sometimes written as SMART), is a monitoring system for computer hard disks to detect and report on various indicators of reliability, in the hope of anticipating failures.
Simplified: Self-Monitoring, Analysis, and Reporting Technology, or S.M.A.R.T. is a system to watch computer hard disks to help stop the risk of failures.