Stress Testing

This kind of test is done to determine the application's robustness in times of extreme load and helps application administrators to determine if the application will perform sufficiently if the current load goes well above the expected load.
Testing conducted to evaluate a system or component at or beyond the limits of its specified requirements to determine the load under which it fails and how. Often this is performance testing using a very high level of simulated load.

For example :
A web server may be stress tested using scripts, bots, and various denial of service tools to observe the performance of a web site during peak loads.