Performance vs. Stress vs. Load testing
More often these terms are interchangeably used in QA testing. Just to draw the line, here’s a definition which I agree with Goranka Bjedov on her Google Techtalk regarding “Using Open Source Tools for Performance Testing”
Performance – measuring how quickly the system responds to a work load. Response time tells everything, proportional to its database, network infrastructure etc.
Stress – measuring when and how the system fail and recover under an extreme load condition.
Load – measuring how the system behaves on a particular load (extremely high and low) over a prolonged period of time.