The concept of “homebrew” for Dungeons & Dragons can be a bit difficult to define, but at its broadest it includes any content used for D&D that is not from an official first-party book published by Wizards of the Coast. This means homebrew could include both custom-made content from an individual Dungeon Master for use in their game, or third-party D&D-compatible published products created under the Open Gaming License.
Read more on screenrant.com