Stress is to check the peak load of the application

Load is to check that how many users are accessing the
application and at the same time to check at which point the
application degrades or failed.

Load testing: During thid type of testing testers will run 
the application on user required load to verify the 
performance of the app.


Stress testing:During this type of testing testers will run 
the app by adding some extra load to an app to find out the 
break down point or maximum capacity of the app which is 
under testing.

Stress Testing:

Testing the application until the system breaks or hangs is 
the Stress Testing.

Load Testing:

Testing the application till the specified load is Load 
Testing

EG: Consider the permissible load is 100

testing from 1 to 100 is load testing and testing from 101 
until where the system breaks is the Stress Testing.

Load testing and stress testing are quite opposite to each
other.

Load Testing: is done to check the maximum capacity of any
application or software to perform its operation, keeping
the standard resources intact. for example: concurrent user
accessing the application throughput, in simple words it is
the process which feeds software with unexpected values and
check how it performs.

Stress Testing: is the process by which we make
software/application starve by reducing the resources
specification and check for the minimum criteria under which
a software can perform. For Example: checking software by
reducing memory etc.