Dynamic Forms was announced in Dreamforce 2019 as one of the features in UI enhancements roadmap in Admin & Lightning Keynotes. It is now available as Non-GA Preview in Salesforce Summer ’20 release
This is going to be a game-changing feature that will give admins and consultants the ability to have granular control on the record pages. You can now declaratively customize sections and fields of the page as per the business requirements. e.g. Show a particular section when a picklist field has a certain value, Opportunity has reached a certain stage, display a section with relevant fields to a particular user profile, etc. So, there are fewer page layouts to maintain.