The acronym HDD stands for Hard Disk Drive, a type of data storage device that uses spinning disks coated with magnetic material to read and write data. HDDs are commonly used in computers and servers for bulk data storage due to their relatively low cost per gigabyte, offering large storage capacities. However, they are generally slower compared to solid-state drives (SSD), which are flash-based and have no moving parts. HDDs remain popular in applications where high capacity is required.