It is about tearing down and rebuilding to achieve dramatic results. Again Wal-Mart and Costco have achieved dramatic results. Meanwhile, Eaton's, who desperately needed re-engineering, also achieved unfortunate dramatic results. Re-engineering focuses on processes that cut across corporate boundaries, however, many companies are structured by departments and tasks. A process is a collection of activities that creates value for the customer.
People performing tasks tend to lose sight of the process and the customer.
For further reading see Reengineering the Corporation by Michael Hammer and James Champy .