OPML的英文全拼是Outline Processor Markup Language，翻译成中文的意思是“大纲处理标记语言”，这是创建在XML上的一种文档保存格式。对于网络日志来说，目前流行的应用方式体现在收集 Blog的RSS来生成订阅列表；订阅列表提供下载、上传服务，方便用户转移自己的订阅列表

OPML (Outline Processor Markup Language) is an XML format for outlines (defined as "a tree, where each node contains a set of named attributes with string values"). Originally developed by UserLand as a native file format for the outliner application in its Radio UserLand product, it has since been adopted for other uses, the most common being to exchange lists of web feeds between web feed aggregators.