Performance Testing: It determines end ot end timing of various time critical business processes and transactions, while the system is under low load, but with a production sized database (all the data you have, actual size of data). Find an optimal time to and from the system and use it as a benchmark. This benchmark is used as a reference against all the future performance/load tests. Without performance testing, we won't know how the application will behave under concurrent and multi-user load.

Load Testing: End-to-end performance testing for an anticipated production load (the number of users/transactions that are meant to be handled by the system at a given time); measure response time under various time critical and business processes. If the response time is greater than the requirement, the test fails. If it is less as compared to the time as required by the client, the test passes. (How does the server behave when too many concurrent user requests come to it?) (3 seconds is the default threshold given to the server as user waits)

Stress Test: How long we run the test matters a lot in a soak test. We don't talk about how long we run the test in a stress test, performance test or a load test. Soak test is running a system of high levels of load for prolonged periods of time. Never have more users that you get from the stress test. The number should be in between the limit you get from a stress test and the load test. A soak test can be 2 days, 2 weeks or a month even; do a weekend test. System must not degrade in performance over a long period of time. This is a verification test. We should have requirements to compare against.