negative testing is nothing but testing the finctionality 
with invalid inputs and conditions

Suneel Answer is correct.

Negative testing is nothing but "Test to Fail"
In this testing we enter invalid data and test that.

eg. you do not have email id in yahoo and you try to login
in yahoo messanger.

It is intended to do  test fail- unacceptable data.
System doesn't do what it is not supposed to do.
For ex. login screen userid input box
It is supposed to take 8 alphanumeric characters
If you enter 9 characters, it doesn't accept.

where we want to put abnormal conditions on the aplication.
ex:invlid form selection
input values out of range
invalid test data selection

Negative testing is done to show that the product does not 
fail when an unexpected input is given. In other words, the 
input values may not have been represented in the 
specification of the product. But, at the end-user level, 
there are multiple scenarios that are encountered and that 
need to taken care by the product. 
The purpose of the negative testing is to break the system.
A negative test would be a product not delivering an error 
when it should or delivering an error when it should not.

negative testing means without getting any errors and if get
the mismatches we will test each and every functionality 

for example:
checking of username and pwd in the login window

Negative testing is simply testing with invalid data, just
to check applications behavior with unexpected inputs.

for example:
If you have to validate "Age" field, your test data should
be numerals between 0 to 200 (I think I expect more :))
But you attempt to validate this field with alphabets OR
special characters it will become negative test data for
negative testing.

Regards,
Rupesh
+919225513854

Negative testing is nothing but testing the application 
against the requirement.

Negative testing is testing an application below and beyond 
of its limits. 
Ex: Entering special characters for the phone number.

Negative testing means entering invalid data and verifying  
for any error message is displayed or not.

Negative testing is nothing but testing the functionality 
of an application by giving the invalid inputs. the main 
intension of the negative testing is we have to test the 
application against the specifications.

Ex: If a text box is accepting only positive integers.

invalid inputs:

1. entering negative values.(-1,-4,-8,-6)
2. entering alphabets.(w,v,y,u,)
3. entering special symbols.(@,$,&,!)

Nagative testing is nothing but testing the application 
with invalid data. 

For instance:
- A field is designed to take between 6-32 characters. 
- when you enter <6 or >32 characters in that field becomes 
invalid input
- when hit enter it should throw you an error message 
saying "enter atleast 6 characters" or something like that.

Negative testing is testing outside the relm of NORMAL 
testing. If a requirement for a vaild age value input is 
between 5 and 50 a negative test would be <5 or >50 
produces a the correct error message along with the correct 
handling process. A NORM condition should be created to 
verfiy and assure that the ages between 5 and 50 inclusive 
produces the correct response and process.

negative testing is nothing but testing the application by 
providing invalid inputs and check for possible errors.