What is the role of "a tester"?

A tester is a person who tries to find out all possible errors/bugs in the system with the help of various inputs to it. A tester plays an important part in finding out the problems with system and helps in improving its quality. If you could find all the bugs and fix them all, your system becomes more and more reliable. A tester has to understand the limits, which can make the system break and work abruptly. The more number of VALID BUGS tester finds out, the better tester he/she is!