Is one who tries to break the developers software and in a 
position to venture the bugs. so that atleast 80% bugs free 
software can deliver.

TO BREAK THE SYSTEM.
ALWAYS TEST FROM THE CUSTOMER VIEW

who covers uncoverd errors and with maximum errors

Good tester should have fallowing qualities

1.Should have a good domain knowledge

2.should think like a customer

3.Never compramise for quality

4.should communicate well

Efficiency of a tester lies in the priority of the bugs he
raises. To raise High priority bugs, the tester should have
a good knowledge on the application. 

Ability of the tester is not measured by the number of bugs
the tester raises but by the priority bugs.

He should have good knowledge on the application
Should think in customers point of view
Should write testcases covering all the requirements
Should raise bugs effeciently to give quality product.
Should not compramise for quality.
Should maintaing good communication and relation with 
developers

Good tester should have fallowing qualities

1.Should have a good domain knowledge

2.should think like a customer

3.Never compramise for quality

4.should communicate well
5.tester have test to break attitude.
6.tester behaves friendly nature both developers and 
testers.
6.tester should have patience

TO FIND OUT THE BUGS AS EARLY AS POSSIBLE AND TO MAKE SURE
TO GET THEM FIXED.