Hi there, & Welcome to Tom's Hardware1
You are probably referring to a HDD and the S.M.A.R.T (Self Monitoring and Reporting Technology). The is an indication there is an error being reported from your hard drive that has exceeded a threshold.
Download and run HD Tune, which can analyze your HDD and look at all the SMART events. It should show you the alert that is being triggered.
It may indicate a failing drive, so it's not something to overlook.