Active Record
In plain terms
A pattern where objects wrap database rows and their operations.
Going deeper
Active Record combines data and persistence so each object represents a row and knows how to save, update, and delete itself. The object is its own data-access layer.
Under the hood
Convenient and concise but couples domain to the database; contrasts with the data-mapper pattern.
Examples
Rails ActiveRecord, Django ORM, Eloquent (Laravel), simple CRUD apps.
Think of it like...
Like a self-filing document that knows how to store and retrieve itself.