Dynamic components are a concept in Ripple that is closely tied to the concept of 'Paragraphs' in Drupal. See the Drupal documentation for Paragraphs.
Dynamic components/paragraphs can be added to pages in drupal (see Key concepts - content types).
In Ripple the raw paragraphs from the Drupal JSON API and 'mapped' to a Vue component, along with the props required for that component to render. This Vue component, along with the associated mapping is what is referred to as the 'Dynamic component'.