Many of the testing experiences, especially product testing, testers will come across situation like executing test cases in
3 Browsers (Chrome,FireFox,IE)
2 Databases (Oracle,SQLSERVER)
4 operating systems(Linux,Windows,Solaris)
etc..
So the total no.of.combination is 3 X 2 X 4 = 24 combinations
If we have even 100 test cases, there comes an exhaustive no of 2400 test cases along with these combinations.
In order to avoid this, we use Pairwise testing, by removing the redundancy in the 24 combinations (in above said example).
How to reduce the redundancy is an important but slightly cumbersome knowledge, but www.testersdesk.com provides a free online tool to create an optimum result on pairwise testing.
Refer: http://www.testersdesk.com/pairwse_testersdesk.html
We have to register to use this tool.