KML全称：Keyhole Markup Language，是基于XML（eXtensible Markup Language,可扩展标记语言）语法标准的一种标记语言（markup language），采用标记结构，含有嵌套的元素和属性。由Google（谷歌）旗下的Keyhole公司发展并维护，用来表达地理标记。根据KML语言编写的文档则为KML文档，格式同样采用的XML文档格式，应用于Google地球相关软件中（Google Earth，Google Map, Google Maps for mobile...），用于显示地理数据（包括点、线、面、多边形，多面体以及模型...）。而现在很多GIS相关企业也追随Google开始采用此种格式进行地理数据的交换。

Keyhole Markup Language (KML) is an XML notation for expressing geographic annotation and visualization within Internet-based, two-dimensional maps and three-dimensional Earth browsers. KML was developed for use with Google Earth, which was originally named Keyhole Earth Viewer. It was created by Keyhole, Inc, which was acquired by Google in 2004. KML became an international standard of the Open Geospatial Consortium in 2008. Google Earth was the first program able to view and graphically edit KML files. Other projects such as Marble have also started to develop KML support.