UNIX for Advanced & Expert Users

A stress run is not exclusive to unix.
You devise a test sequence which will put the computer under stress, usually to simulate the expected maximum load on the computer before giving it to live users.

Thanks a lot for your reply now I know what stress is can you please tell me how we can perform this in Unix environment any help in regards will be highly appreciated .

I don't think you quite understand. a stress test is a category of test, not some sort of benchmark. What you do depends on what you're testing, and of that you've told us nothing. If you're stress-testing a DNS server, generate a lot of DNS activity. Stress testing a file server, generate a lot of file activity. stress testing a web server, generate a lot of network traffic. and so on.

Thanks for clearing my concept about Stress can you please tell me is their any tool available to perform stress on DNS and file server in unix

For testing DNS, there are few toolsets you can check : TXDNS, an aggressive multithreaded DNS digger., BIND DLZ FAQ's, dns-grind - pentestmonkey.net.
For file server - there are many tools, depending on what exactly you are trying to achieve, Iozone Filesystem Benchmark is a good start, especially the 'fileop' that's included in the kit.