Performance tests reveal how a system behaves and responds during various situations. A system may run very well with only 1,000 concurrent users, but how would it run with 100,000? In terms of performance, we wish to achieve high speed, scalability, and stability of the system. There are several types of performance tests in which each simulates a different possible user scenario.
Load testing checks how systems function under a heavy number of concurrent virtual users (simulating heavy load volumes) as they perform transactions over a certain period of time.
Stress testing checks the upper limits of your system by testing it under extreme loads, thus finding the system breaking point. These tests also examine how it recovers when going back to normal usage.