Narrow and Discard
At the bottom of your search results screen, click the "Refine" button. You will find "Narrow" and "Discard" buttons in the blue bar. You can use these to help refine your search results.
Narrow: As you go through your search results, there may be only certain ones you want to keep. Click the check box next to each listing you want to keep. Click the "Narrow" button. This will remove all listings from your search results that you did not check, so that you can more easily focus on the listings that interest you. In other words, you "narrowed" your search results.
Discard: This works the opposite of "Narrow." Click to select any listings that you want to remove from your search results. Click the "Discard" button. The listings you selected will be dropped from your search. After using the "Discard" button, a new button will appear labeled "Un-Discard." You may click this button to return your discarded listings to your results.