Test case is for to test a specific functionality of an 
application where as test matrix/tracebility matrix is used 
when ever there is an ambiguity or contravesal situation 
arieses then one has to show all the relevent document to 
defined himself  for example .suppose we got a defect  for 
that we need to show all the revelent doc. like 
BDD,UCD,FPD,MTCD,DTCD,TCD etc,. as proof for which test 
case we got that bug