Regression Testing:
It is a process where the tester ensures that the software is satisfying the requirements on each and every release. Here the testing is done on already tested functionality and making sure it works now also.
Retesting:
It is a verification process where the tester makes sure that the defect which was marked as fixed by the developer is working as expected, so as to close it.
1. Development is incremental rather than sequential.
2. People and interactions are emphasized, rather than processes and tools.
3. Working software is the priority rather than detailed documentation.
4. Customer collaboration is used, rather than contract negotiation.
5. Responding to change is emphasized, rather than extensive planning.
Rapid, continuous delivery
Late changes in requirements are allowed
Close, daily cooperation between business people and developers
Regular adaptation to changing circumstances