###This is called "Local Datasources"
This is called "Local Datasources"
Essentially it is a way to help prevent massively bloated shared folders for content that really only appears on the page in question.
It is (mostly) supported out of the box in Sitecore, with only a few minor UI adjustments required for a good experience.
One example here: Local Datasources module for Sitecore Experience Editor and here: SITECORE LOCAL DATASOURCES