Stess testing is beyond the limit how the system is working.
where as load testing is upto the limit how the system is
working
volume testing is volume of data transfer will be validated
.the amount of volume time taken to upload a file

Load testing is the process of subjecting an application to 
a work level approaching the maximum limit. This is 
basically to test the reliability of the application. This 
is a part of more general process called 'Performance 
Testing'. 

Eg: Assigning many jobs to a printer in a queque.

Load testing can be conducted in two ways:

1. Longevity Testing(Endurance Testing): This evaluates a 
system's capability to handle a constant moderate load for 
a long time.

2. Volume Testing: This evaluates a system's capability to 
handle huge load for a short time.

Stress Testing: Evaluates the extent to which a system 
keeps working when subjected to extreme work loads or when 
some of its hardware or software is comprimised. The 
primary goal is to determine the maximum amount of work a 
system can handle without breaking.

Stress: More than Max input given to the application
Load:  max input given to the application

volume: volume of data transfer will be validated