Chkdsk (Check Disk) is a Windows utility that checks the file system and disk for errors, and repairs any issues it finds. It scans the disk for bad sectors, detects and fixes file system errors, and marks any corrupt files as unusable. Chkdsk also displays a summary of the scan results, including the total disk size, used space, free space, and any errors that were found and fixed during the scan. Running chkdsk regularly can help prevent data loss and keep your system running smoothly.