CHKDSK is a built-in Windows utility that checks the integrity of a computer's hard drive. It scans for file system errors and bad sectors, helping to identify and fix issues that could lead to data loss or system instability. Users can run CHKDSK from the command prompt or through the properties menu of a drive. When CHKDSK is executed, it can repair problems automatically or provide a report of the findings. This tool is essential for maintaining the health of a computer's storage and ensuring that files remain accessible and intact over time.