Re-Testing: Is the Process where Test engineers (Testers) are conformed that application is working fine (there are no bugs or there is no more regression Testing).Then Testers are going to test the entire application with different input values to get accurate expected values (Result).

Regression Testing: Is the process when Tester found a bug and the testing process is stopped or it is abstracting testing...then developers are going to Fix that Bug andThis time tester are going to Testing the whole application from just previous step where the bug is found and resloved.And also going to check for the affects of that modification done on application.