What is the difference between a data warehouse, Delta Lake, a data lake, and a data lakehouse?

A data warehouse is a structured, schema‑on‑write system optimized for fast analytical queries; data is cleaned, transformed, and stored in tables. A data lake stores raw, unstructured or semi‑structured data in object storage (e.g., S3) with a schema‑on‑read approach, allowing flexible ingestion but requiring more effort to query. Delta Lake is an open‑source storage layer that adds ACID transactions, schema enforcement, and time‑travel to a data lake, enabling reliable batch and streaming workloads on lake data. A data lakehouse combines the best of both worlds: it uses lake storage for raw data but provides warehouse‑like features such as ACID guarantees, schema enforcement, and a SQL engine, allowing users to run analytics directly on lake data without moving it. In short, warehouse = structured + fast queries; lake = raw + flexible; Delta Lake = lake + ACID; lakehouse = lake + warehouse features.