A disk array is a disk storage system containing multiple disk drives. It is different from a disk enclosure, in that an array has cache memory and advanced functionality, like RAID and virtualization.
Typically a disk array provides increased availability, resiliency and maintainability by using additional, redundant components (controllers, power supplies, fans etc.), often up to the point when all single points of failure (SPOFs) are eliminated from the design. Additionally, those components are often hot-swappable.