while doing testing if any action is not performed, we say 
it is a defect. it will send to developer to fix

Thanx 4 reply..
but i need some more info.. i'll reword my q "What is 
defect tracing? how it' done?"

if the application doesnot process as given in the BRS and
SRS Documents.

Tracing a Defect is nothing but Deviation of the Customer 
requirement in the application.

If Customer Requirement is not performing its function or 
not available in application, i.e. called Defect.

Defect Tracking means... Ensure that the Defect is related 
to which Test Case. You should able to find which defect is 
related to which Requirement, Tracking the defect with 
respect to Test Cases... you can maintain the documents 
with Hyperlinks to desired Documents 

for e.g. Functional Requirement Specifications Document
         Use Case document
         Master Test Case Document
         Detailed Test Case Document
         Defect Profile Document
if you maintain according to your desired documents with 
hyperlink, you can easily Trace back Which Defect is 
related to which Requirement...

Implementing  the concerned test cases on the concerned
functionalities ,If it behaves as per the customer
requirement.We can conclude that it has no defect,otherwise
it is a defect

tracking the defect means trace the defect to it's complete 
life cycle . I mean to say if tester find the defect ( 
deviation from requirement ) he/she will assign it to 
developer with priority & severity . Developer fixed it in 
these procedure defect has lot of status like new , open , 
reopen , fixed, differed , rejected , verified ,closed .TO 
keep the track of defect from new to closed is called 
defect trace

Tracing a defect means...

what is the status of the defect in its life cycle and, for 
which requirement and which test case it is reported as 
defect!

we can trace a defect using a defect traking tool,r by 
using a excel sheet.

As soon as u find a defect.you will track that defect Using 
a Bug Tracker tool and give the Status as New.If the 
Developer Fixes he gives the status as Fixed.After Fixing 
the tester will retest and give the status as Closed(If he 
feels defect is fixed).the Entire Process will be carried 
out in a Bug Tracking Tool(depends on the Company which 
tool tey are using).

Through Traceability matrix we can trace which part of the 
software(requirement) is failed(defect).

Traceability Matrix:
Traceability matrix is a document defines mapping between 
customer requirements and prepared test cases.

Anything which is 
- Wrong
- Missing
- Extra

in application from SRS and FRS