6. layout file types

1.Page layout

<layout xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/page_layout.xsd">
    <update handle="1column"/>
    <referenceContainer name="columns">
        <container name="div.sidebar.main" htmlTag="div" htmlClass="sidebar sidebar-main" after="main">
            <container name="sidebar.main" as="sidebar_main" label="Sidebar Main"/>
        </container>
        <container name="div.sidebar.additional" htmlTag="div" htmlClass="sidebar sidebar-additional" after="div.sidebar.main">
            <container name="sidebar.additional" as="sidebar_additional" label="Sidebar Additional"/>
        </container>
    </referenceContainer>
</layout>

2.Page layouts declaration

<page_layouts xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/PageLayout/etc/layouts.xsd">
    <layout id="1column">
        <label translate="true">1 column</label>
    </layout>
    <layout id="2columns-left">
        <label translate="true">2 columns with left bar</label>
    </layout>
    <layout id="2columns-right">
        <label translate="true">2 columns with right bar</label>
    </layout>
    <layout id="3columns">
        <label translate="true">3 columns</label>
    </layout>
</page_layouts>

3.Page configuration

4.Generic layout

<layout xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:noNamespaceSchemaLocation="urn:magento:framework:View/Layout/etc/layout_generic.xsd">
    <update handle="formkey"/>
    <update handle="adminhtml_googleshopping_types_block"/>
    <container name="root">
        <block class="Magento\Backend\Block\Widget\Grid\Container" name="googleshopping.types.container" template="Magento_Backend::widget/grid/container/empty.phtml"/>
    </container>
</layout>

http://devdocs.magento.com/guides/v2.0/frontend-dev-guide/layouts/layout-types.html