What is the difference between ref and source functions?

The ref() function in dbt is a reference to another dbt model, creating a dependency that dbt tracks for build order and incremental logic. It also allows you to use the model’s name in a portable way across environments. The source() function, on the other hand, points to a table that lives outside the dbt project, such as a raw table in a staging schema. It is used for documentation, tests, and to keep track of lineage, but it does not create a build dependency. In short, ref() is for internal models, source() is for external tables.