Liquid Template Variables - page description
From Spiffy Stores Knowledge Base
The Liquid template variable page_description returns the current page description that can be used to generate the <meta> description HTML tag.
This can be used in your theme.liquid file to provide a page description for Search Engine Optimization
<head>
<title>{{shop.name}} - {{page_title}}</title>
<meta name="description" content="{{ page_description }}"/>
...
</head>
The tag is automatically generated based on the type of page being displayed. A custom value can be provided for Products, Collections, Pages, Blogs and Articles through the SEO configuration option on the edit pages for these items.