What is a 'Foreign Wrapper' (FDW) in PostgreSQL?

What is a 'Foreign Wrapper' (FDW) in PostgreSQL?

Approach: Explain querying external data as if it were local.

An extension that allows a PostgreSQL database to access and query data stored in external data sources (like other SQL databases, CSVs, or Redis) using standard SQL.

Follow-up: Is data physically stored in the local database?

Key concepts: postgres, virtual tables.