There are three different methodologies in testing 1.Black
box testing 2.White box testing 3.Grey box testing. And
testing techniques are 1.Boundary value analysis 2.Eqivalant
class partition 3.Error guessing 4.Cause_Effect graph.
Black box testing: Testing which performs with out the
internal structure knowledge and with the functional
knowledge of the application.
White box testing: Testing which performs by knowing the
internal structure of the application.
Grey box testing:A black box tester who performs the white
box testing is considerd as grey box tester. That means
combination of both.

if the defect is logged and is not solvable by developers, 
then the developers report this as known issues in the 
build. so the defect age in these cases can be said to have 
a lifetime of from when it was logged to time when it was 
reported as a known issue by developers and confirmed by 
testers.