What is Yelp?from http://www.yelp.com.au/faq#what_is_yelp
Yelp is an online urban city guide that helps people find cool places to eat, shop, drink, relax and play, based on the informed opinions of a vibrant and active community of locals in the know. Yelp is the fun and easy way to find, review and talk about what's great — and not so great — in your world.
From Bing Blog
http://www.bing.com/community/site_blogs/b/search/archive/2012/06/14/bing-and-yelp-help-you-do-more-with-local-search.aspx
Yelp Blog
http://officialblog.yelp.com/2012/06/yelp-to-power-bing-local-search.html