System Testing proves that the system meets all objectives. 
This type of testing provides an external view of the 
system in such a manner that would be easy to use for the 
user since user is not concerned how the system response 
and works as only requires that the system functions 
properly. It can be also referred to as verification 
testing when the testing occurs in non –live test 
environment. This type of testing is based on system 
requirements and operations document. This type of testing 
would ensure that the software product operates in all the 
different environments where a program may operate like 
various operating systems, various Internet browsers, 
various Internet speed and various resolutions.

functional testing + non-functional testing is called system testing.

system testing is the process of testing the functionality
behavior of the entire application right from the first
module to the end of last module.under this functional
features,non-functional features,performance,comparability
can be checked.objective is to check the completeness and
correctness of the application.