Normally if you test one application u have to test both 
positive and negative testing. for example if u take login 
screen if the enter valid username and password that is 
positive testing if the username is invalid and password is 
invalid then that is negative testing


correct me if i am wrong

Negative testing involves applying negative inputs to the 
application with the intension of finding errors in the 
application.

Negative testing is aimed at showing software does not work.

Testing the application againest of the requirement is 
called negative testing

Ex: for UID you must have to enter 8 letters but you 
entered 6 letters and testing is system is accepting it or 
not if it's accepting then it's a deffect. This is called 
negative testing.

Testing the application for fail conditions, negative 
testing is testing the tool with improper inputs.
For example entering the special characters for phone 
number.

Negative testing is the conducting testing with the tets 
scenarios in which cases the software should fail in its 
functionality