The term, volume testing, is often used synonymously with 
load testing. Load testing is a blanket term that is used 
in many different ways across the professional software 
testing community.

Volume Testing refers to testing a software application for 
a certain data volume. This volume can in generic terms be 
the database size or it could also be the size of an 
interface file that is the subject of volume testing.

Where as Load testing is a stress given to the system.

as per my knowledge 

load testing is total no of users can access the 
application at a time 

volume testing means how much data volume that can be 
stored in the database of our project

In Load Testing we test the response time of the 
application with respect to the no of users.Response time 
shouldn't increase if no. of user increase, to a specified 
limit in SRS
say if users exceed to 1 million respone time shouldn't 
exceed 3sec.

In Volume testing the response time of the application is 
tested with respect to the data.If the data is increased in 
database the response shouldn't exceed the one mentioned in 
SRS