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.
Refer: Wiki https://en.wikipedia.org/wiki/Keyhole_Markup_Language
1) Download Shape File Ex: http://ippuc.org.br/geodownloads/SHAPES/DIVISA_DE_REGIONAIS.zip
Convert Shapefile to kml in QGIS:
2) More Details (here) http://www.igismap.com/convert-shapefile-kml-qgis/ .
3) Open KML and add the following data for each point..
This a mandatory step, without the cordinate Z LeaFlet(http://leafletjs.com/) will not work.