soak testing, also known as reliability testing is a type 
of stress testing in which testing will be done for longer 
periods of time inorder to check application's stability.

Soak testing is one type of Performance testing in which we 
can test the stability and response time of the application 
by applying the designed load for a longer time. in this 
case the time duration may be normally 72hrs to 120 hrs.

soak testing is nothing but endurance testing. appling 
customer expected load for long time on the build 
continuously depending on our interest of interval period 
in sec whether they are fix sec or random seconds or as 
soon as the first iteration completes apply the second 
iteration and continue.

Testing the application continuously for several hours  to
identify its stability.

Soak testing involves testing a system with a significant 
load extended over a significant period of time, to 
discover how the system behaves under sustained use.

For Example: a system may behave exactly as expected when 
tested for 1 hour. However, when it is tested for 3 hours, 
problems such as memory leaks cause the system to fail or 
behave randomly.

Soak testing (Also Known as Endurance Testing) is running a 
system at high levels of load for prolonged periods of 
time.  A soak test would normally execute several times 
more transactions in an entire day (or night) than would be 
expected in a busy day, to identify any performance 
problems that appear after a large number of transactions 
have been executed.