A Hard Disk Drive (HDD) is a traditional storage device that uses spinning disks to read and write data. It stores information magnetically, making it suitable for large amounts of data at a lower cost. However, HDDs are generally slower and more prone to mechanical failure due to their moving parts. A Solid State Drive (SSD), on the other hand, uses flash memory to store data, which allows for faster access and improved durability since there are no moving parts. SSDs are more expensive per gigabyte than HDDs but offer better performance, making them popular for modern computers and devices.