Data migration
Post-migration: After data migration, results are subjected to data verification to determine whether data was accurately translated, is complete, and supports processes in the new system. During verification, there may be a need for a parallel run of both systems to identify areas of disparity and forestall erroneous data loss. Additional documentation and reporting of the migration project is conducted, and once the migration is validated complete, legacy systems may also be decommissioned. Migration close-out meetings will officially end the migration process.
Data processing
Data processing is, generally, "the collection and manipulation of items of data to produce meaningful information." 
In this sense it can be considered a subset of "information processing", "the change (processing) of information in any manner detectable by an observer." 
The term Data Processing (DP) has also been used to refer to a department within an organization responsible for the operation of data processing applications.