A company sells furniture. A customer goes to their website, clicks on the search bar, and types in “couches.” However, the company refers to these items as “sofas.” A good search algorithm should be able to direct the user to the sofas page. If they are notified with “sorry, no matches found,” or if the results are irrelevant, they might hit the back button, or they might even bounce (the Google Analytics term for leaving a website).