Soak testing involves testing a system with a typical production load, over a continuous availability period, to validate system behavior under production use.
[1] It may be required to extrapolate the results, if not possible to conduct such an extended test.
For example, if the system is required to process 10,000 transactions over 100 hours, it may be possible to complete processing the same 10,000 transactions in a shorter duration (say 50 hours) as representative (and conservative estimate) of the actual production use.
However, when it is tested for three hours, problems such as memory leaks cause the system to fail or behave unexpectedly.
Some companies may soak test a product for a period of many months, while also applying external stresses such as elevated temperatures.