Redundant Array of Independent/Inexpensive Disks (RAID) is a technology that allows storing data across multiple hard drives. The purpose of RAID is to achieve data redundancy to reduce data loss and, in a lot of cases, improve performance. 

RAID was created in 1988 in order to deal with costs of high-performing disk drives. The inventors argued that an array of inexpensive disks could outperform a single expensive disk, which was no doubt a huge problem when 10MB of storage cost upwards of $100. RAID allows for data to be stored on multiple disk drives at once, though a RAID setup will appear to, say, Windows 10, as a single disk.