Traceability matrix is nothing but mapping FS to Test 
cases.This ensures that u have written enough test cases 
covering all the functionalities.

Traceability matrix is a table which is used to map the 
baselined documents like testplan,teststrategy,testcases 
and defect profile documents.

It is a doucment showing the releation ship  between the 
docments or test cases 
by looking at the these traceability matrix we can check 
all testcase or covered or not
by looking at these tracebality matrix we can all the 
testcases are written as per the srs brs documents.

It is a document where requriment specfication is mapped to
functional specification.functional specification  is mapped
to  source coding.source coding is mapped to test case

Traceability matrix is a table which correlates the complete
SRS to testcases written for testing. This table is useful
in identifying whether all the testcases are covering the
requirements of the SRS, inturn the requirements of product

A traceability matrix is a document, usually in the form of 
a table, that correlates any two baselined documents that 
require a many to many relationship to determine the 
completeness of the relationship. It is often used with 
high-level requirements (these often consist of marketing 
requirements) and detailed requirements of the software 
product to the matching parts of high-level design, 
detailed design, test plan, and test cases.

Common usage is to take the identifier for each of the 
items of one document and place them in the left column. 
The identifiers for the other document are placed across 
the top row. When an item in the left column is related to 
an item across the top, a mark is placed in the 
intersecting cell. The number of relationships are added up 
for each row and each column. This value indicates the 
mapping of the two items. Zero values indicate that no 
relationship exists. It must be determined if one must be 
made. Large values imply that the relationship is too 
complex and should be simplified.

To ease the creation of traceability matrices, it is 
advisable to add the relationships to the source documents 
for both backward traceability and forward traceability. In 
other words, when an item is changed in one baselined 
document, it's easy to see what needs to be changed in the 
other.