求教专利编号相关的问题

Plaintiff Honeywell is the lawful owner of United State Patent No. 7,320,110,which was

duly and legally

issued by the <st1:country-region w:st="on">United States Patent and Trademark Office on ...
我用这句话中的专利号7,320,110，在Google Patent http://www.google.com.hk/search? ... tbo=1&hl=en 中搜索，找到了专利文件，问题是我注意到这份文件第一页右上角的Patent NO标注的是 7,320,110 B2. 请问各位，这个编号B2说明了什么？有特殊含义吗？

授权之前曾公开的专利。

冷泉村人:授权之前曾公开的专利。 (2011-12-23 13:04)

thanks