Yelp is an online directory (much like the Yellow Pages) which lists local businesses by their location and service. There are hundreds of these sorts of websites across the Internet but Yelp is somewhat special because it is the service used by Apple's iPhone in "Siri". That means, if someone were to ask their iPhone "where can I get lunch?", it would be pretty nice to have your business pop up!
Now you know what Yelp is and why it's significant, it should be mentioned that at this stage, Apple haven't enabled this type of local business searching in Australia (it's only in the USA). However, one could argue it's only a matter of time, so it's worth making sure your business is listed.
To find out more about Yelp, just click over and visit their website.