The Tiles '.mainTemplate' sets up the default layout and the other two definitions extend the main template and just set their body.
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE tiles-definitions PUBLIC
"-//Apache Software Foundation//DTD Tiles Configuration 2.0//EN"
"http://tiles.apache.org/dtds/tiles-config_2_0.dtd">
<tiles-definitions>
<!-- Default Main Template -->
<definition name=".mainTemplate" template="/WEB-INF/templates/main.jsp">
<put-attribute name="title" value="Simple Tiles 2 Example" type="string" />
<put-attribute name="header" value="/WEB-INF/templates/header.jsp" />
<put-attribute name="footer" value="/WEB-INF/templates/footer.jsp" />
<put-attribute name="menu" value="/WEB-INF/templates/menu.jsp" />
<put-attribute name="body" value="/WEB-INF/templates/blank.jsp" />
</definition>
<definition name="index" extends=".mainTemplate">
<put-attribute name="body" value="/WEB-INF/jsp/index.jsp" />
</definition>
<definition name="info/about" extends=".mainTemplate">
<put-attribute name="body" value="/WEB-INF/jsp/info/about.jsp" />
</definition>
</tiles-definitions>