Migrate is a core module that provides a framework for importing, transforming, and saving content in Drupal. It replaced the older Migrate D2D approach used in Drupal 7.
Migrations are defined in YAML with three main parts. The source describes where data comes from, the process describes how to transform each field, and the destination describes what entity to save.
Migrate supports source plugins for CSV, XML, JSON, SQL databases, and Drupal content. Process plugins transform values, handle references, and apply default values. Destination plugins save to content types, users, taxonomy, and more. Combined with Migrate Plus and Migrate Tools, you get a full migration workflow including running, rolling back, and monitoring. It is one of the most powerful content migration tools available in any CMS platform.