A block theme, or block-based theme, is the same as a full site editing (FSE) theme.
A classic theme is one that doesn’t work with full site editing.
Terminology
Whether you are a site owner or a developer, there’s new lingo to learn. Get started with our Full Site Editing glossary.
Differences in User Experience
If you use a classic theme, you will still be using the block-based editor for your posts and pages, but you’ll be dependent on your theme to provide editing capabilities for other parts of your site, like the header, footer etc.
Classic themes utilize either their own custom options panel, or the WordPress customizer to provide design and other controls.
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