point-in-time copy:    A fully usable copy of a defined collection of data that contains an image of the data as it appeared at a single point in time. The copy is considered to have logically occurred at that point in time, but implementations may perform part or all of the copy at other times (e.g., via database log replay or rollback) as long as the result is a consistent copy of the data as it appeared at that point in time. Implementations may restrict point in time copies to be read-only or may permit subsequent writes to the copy. Three important classes of point-in-time copes are split mirror, changed block and concurrent. Pointer remapping and copy-on-write are implementation techniques often used for the latter two classes. cf. snapshot.

See also: Operational Recovery