Imagine that your website is concerned with the care and feeding of cats and that you have decided to add a search on Topic. You must define an indexed variable (we'll call it Topic) before you can run searches. One topic might be Grooming, what do you expect your users to type in to locate this story? It might be the exact case sensitive literal word 'Grooming' or perhaps you are more forgiving and would accept 'grooming'. How about 'grOOMing'? It's more user friendly to be case insensitive, so you would probably set Search ignores Case for this variable.