Metrics are used to measure the strength of testing process

These are used by Management people not b testers

Test Metrics is a process of defining how the testing should
be in the future.

Test Metrics is something like a 'Measurement'.

Prepared by the Project Manager (along with Team Leader).

Certain things that Manager will be focusing like:

-> Number of Bugs found
-> High priority bugs
-> Time limit to resolve the Priority bugs
-> Bugs found at UAT
-> Report about how many test passed / failed..so on so forth

-------Plz correct me if I am wrong

While testing a product, test manager has to take a lot of 
decisions like when to stop testing or when is the 
application ready for production, how to track testing 
progress, how to measure the quality of a product at a 
certain point in the testing cycle? Testing metrics can 
help to take better and accurate decisions

Lets start by defining the term 'Metric'
A metric is a mathematical number that shows a relationship 
between two variables. Software metrics are measures used 
to quantify status or results.

Test metrics is a measuring tool to measure the quality of
the product during the execution phase. Usually it is a
template prepared in the excel sheet.
Test metrics contains
Total test, Test run,No of test cases executed, No of test
cases passed, No test cases failed and no of test cases
deferred.