There are 3 types of regression

1)Unit regression : nothing but retesting ie testing to

make sure that bug is properly fixed or not / new enhanced

feature is working according to the specification.

2)Regional Regressin : Unit regression + testing the impact

area to make sure that bug fixation or new feature not

affecting the unchanged module.90% of the case industry

prefers this regression.

3)Full Regression : when it is difficult to identify the

impact area after the bug fixation or after adding the new

feature ,instead of wasting time in identifying the impact

area they will go with full regression.