ActiveRecord is an ORM

Active record is a ORM(Object Relational Mapping) library. This means that even though you’re interacting with a database in your Rails app by writing User.create or User.find_by you’re not really writing SQL but writing with a DSL(Domain Specific Language) called ActiveRecord to compile SQL code to interact with the SQL database. So in console I type

 User.find_by(id:1)

which uses the ActiveRecord Library to execute this hidden SQL code into the database:

 SELECT * FROM users WHERE id = 1 LIMIT 1;
 

This outputs an ActiveRecord hash containing a user found by the query in the database.

#<User id: 1, nickname: "Pookie", name: "Renan", user_profile: "http://steamcommunity.com/id/the_real_renan/", user_image: "https://steamcdn-a.akamaihd.net/steamcommunity/pub...", user_location: "Miami, FL, US", uid: "76561198287309916", provider: "steam">

Here we use the development database from SteamFriend.me to fetch a user with an id of 1.

You can find out more on the official Rails ActiveRecord ORM here