Bricks — is a new way of building pages on top of Entity Reference, Display Modes, Layout API, tabledrag.js and Flat Tables. Everything is in Drupal core that makes Bricks ultra-lightweight and developer-friendly.
In terms of concept Bricks is a new generation of Paragraphs, an alternative to Panelizer and a good friend to ECK, Inline Entity Form and your favorite WYSIWYG. Shortly, it allows you to nest Entity Reference field items using Drupal drag & drop UI (exactly like for menu or taxonomy items).