load testing is to check the project is supporting to the 
decided max users or not.
where as stress testing is checking the project how much 
max load the project can support.

Load Testing is performed to check application response
under maximum load. This type of testing is performed to
check maximum capacity of the application with maximum
number of users.
while Stress Testing is performed to check the application
response beyound the load. Main goal of this testing is to
identify the point where system will crashed. This type of
testing is performed as Negative Testing

Load Testing: Verifying whether the application supports 
customer expected load at customer expected configuration 
system.

Stress Testing:Finding max limit of load at customer 
expected config system.
In detail stress testing is done to evaluate the system 
beyond the limits of specified requirements to ensure that 
the system doesnt break.Stress testing is done to find out 
if the products behaviour degrades under extreme 
conditions.For this the product is overloaded to find out 
its behaviour.It helps us to understand how the system 
could behave under extreme conditions like insufficient 
memory,inadequate resources etc.This helps to know the 
situations under which the tests fail so that max limits in 
terms of users,no. of transactions etc can be know.

Load testing: The execution of our app. build is going to 
support customer expected configuration and customer 
expected load to estimate the speed of processing of our 
app. build.
 
Stress testing : The execution of our app. build is going 
to support customer expected configuration and various load 
interfaces from low to peek to estimate the speed of 
processing of our app. build.