Maybe you've heard of "entities" in Drupal 7, wondered what they were, and wanted to learn the underlying concepts. Leveraging the Entity API lets you create more lightweight and flexible solutions.
The Drupal community often compares site building through configuration to a favorite childhood toy: LEGO bricks. We can build Entity types, which can make Bundles, to which we can add Fields and then create Entities. This article explains the relationships between Entity types > Bundles > Fields > Entities. This was one of the most important changes of Drupal 7, and brought components from some well-loved contributed modules -- such as CCK -- into the core system.
The illustration below shows some examples of Entity types included with Drupal 7, with some example entities:
Let’s take a closer look at these concepts. It’s sort of a chicken-and-egg thing, one doesn’t exist without the other.