Lytics considers every piece of content as a "document", and calls the collection of every document a "corpus". Lytics automatically processes every web page for an account's site, where each web page is a "document". In the Lytics app, documents are surfaced in association with topics and in content recommendations.
Keep in mind that the Lytics Content Affinity Engine isn't limited to your website content. All sorts of content can be sent to Lytics, including product catalogs to power Product Recommendations.
You can Find a Document in the Lytics UI, and view the profile for a particular document including its metadata, topics, and other information. This page allows you to sort by which stream the content is collected from and see the different fields and values captured. To see if this document is used in any Content Collections, you can view the Collections tab.