after completion of sucessful functional testing on 
software build, the test engineers are concentrating on 
extra characteristics of that software testing.such as user 
interface testing,realibility testing configuration 
testing...

Non-functional testing covers that part of the application 
in which the functionality of the application is 
irrelevant. For example, look and feel[GUI] testing.

In Generic Terms the word Non-Functional in Testing meant 
to Performance, Load, Stress, Volume.... Testings.

In Manual - What Ms.Devi had mentioned above is Field Level 
Validations part of Unit Testing which is supposed tobe 
done by the development team.

As per my knowledge Non-Functional in Manual Testing 
relates to Testing the functionalities which is not 
available in the Requirement Document. 
For E.g. 
In a Masters Module checking - Duplication of Records in 
Add / Edit Screen
Soft / Hard Delete - Delete one record and try to add the 
same record - if its soft delete it shows already exists 
but user cannot view the record in the interface - status 
were changed in Backend
Important one is Referential Integrity
Parent Level module cannot be deleted if it contains any 
records in child level modules.
and Security Testing ( Check Cookies were deleted 
properly ) -- Big Topic will discuss separately

Any queries send email to s.nandakumar at sify dot com
98844-17981
Regards
Nanda

Testing requirements of a system that do npt relate to 
functionality,this includes performance, security, 
reliability, load, volume, sociability, failover and 
recovery, stress testing.

Functional testing- its all the part of requirements 
documents, business document, testplans etc, functional 
testing will relate to all part os the page interacting 
with the other page with the exact mapping of variables. 
this testing process will include the actual business which 
is expected by te customer.
Non Functional testing- its a part of checking the 
stability in the appication, for instance how does the 
variables reflect if the data entered is not relevent to 
the data which specified. non functional testing involves 
adhoc testing process to check the stability. non 
functionality testing involves different ways meaning it 
can be testing the accespatence after changing the 
environment changing the popup messeges ect.

This is to test the features and facilties and also the 
stability of the application - which are not directly 
related to the business functionaly but are essential. This 
covers:
- Performance, load, stress and volume testing
- Security (System and application) testing
- Relaibility testing
- Fail recovery testing (at application level)

At times this is also extended to other testing such as 
adaptability testing, configuration testing etc. But it 
depends upon the specific organisation and the needs.

Non-functional testing is the testing of a software 
application for its non-functional requirements. The names 
of many non-functional tests are often used interchangeably 
because of the overlap in scope between various non-
functional requirements. For example, software performance 
is a broad term that includes many specific requirements 
like reliability and scalability. this testing can be start 
as soon as s/w is developed. it bassically includes GUI 
features of a s/w

Non-functional testing includes:

Compatibility testing 
standard testing
Documentation testing 
Endurance testing 
Load testin
Performance testing
Security testing 
Scalability testing 
Stress testing 
Usability testing 
Volume testing 
             and more but depends with the environment and 
requirement.