Disk failure occurs when a storage device, such as a hard disk drive (HDD) or solid-state drive (SSD), stops functioning properly. This can result from physical damage, wear and tear, or electronic malfunctions. When a disk fails, it can lead to data loss, making it difficult or impossible to access files stored on the device. Common signs of disk failure include unusual noises, slow performance, and error messages when trying to access data. Regular backups and monitoring tools can help prevent data loss and identify potential issues before they lead to complete failure of the disk.