A Hard Disk Drive (HDD) is a type of storage device used in computers to store and retrieve digital information. It consists of one or more spinning disks coated with magnetic material, where data is written and read by a moving arm with a read/write head. HDDs are commonly used for storing operating systems, applications, and files due to their large capacity and relatively low cost. HDDs are different from Solid State Drives (SSDs), which use flash memory and have no moving parts. While HDDs typically offer more storage space for the price, they are generally slower and more susceptible to physical damage compared to SSDs.