Is Beaver Builder a plugin or a theme?

Both! 

Our standard package includes just the Beaver Builder plugin. The Beaver Builder editor is a visual layout tool to help you build layouts and add content to WordPress pages. The Beaver Builder editor works with most any theme, but see the list of incompatible themes in the Related Article below.

Our Pro and Agency packages include both the Beaver Builder plugin and the Beaver Builder Theme. The Beaver Builder Theme has lean code, great customization options, and of course it integrates perfectly with Page Builder. And you can go straight to our stellar Support team for any questions, whether it pertains to the plugin or the theme.