A CMS and a website builder are similar because they are both used to build and publish websites. Both of their user experience are also quite beginner-friendly.
These days, you can call a CMS a website builder and no one will have a problem with it. In fact, many people have referred to WordPress as a website builder.
But if you want to get technical with it, then one difference is that a CMS usually doesn’t come with a hosting service, as you must purchase one yourself.
On the other hand, a website builder (like Wix or Squarespace) typically includes a cloud-based hosting service that’s managed for you.
Additionally, a CMS typically has a large collection of plugins and themes made by third-party developers, so their customization is virtually limitless. This is because a lot of CMSs are open-source.
Meanwhile, website builders usually aim to be all-in-one solutions, where users don’t need to install many apps to use them.