Unallocated Space
Storage regions not currently assigned to live filesystem objects, potentially containing deleted or residual data.
Digital-Forensics Context
Unallocated space contains filesystem regions not currently assigned to live objects. Deleted file contents may remain there until the blocks are reused, which makes carving, keyword search, and other residual-data techniques possible on an acquired image.
Evidence Boundary
SSD TRIM, encryption, controller behavior, and background garbage collection can reduce or eliminate physical persistence. A logical image also does not necessarily expose residual data that might exist at lower flash-management layers.