A data warehouse is a system that combines multiple operational data system (usually OLTP systems) together into one big database. For example, BigQuery is a data-warehouse.
These warehouses are intended to use with an OLAP system where you aggregate over this data and find novel insights and are thus a analytical data system.
A big advantage is that these warehouses combine the data from other systems in one place. If you wouldn’t combine them, connecting, normalizing and aggregating them ranges from hard to impossible.
To normalize the data or schemas, processes like extract, Transform, Load are often used, whilst the data is loaded in batches.
When you add files (images, videos) or other non relational data, we usually talk about data lakes.
Reference
Kleppmann, Martin, and Chris Riccomini. Designing Data-Intensive Applications: The Big Ideas behind Reliable, Scalable, and Maintainable Systems. Second Edition, O’Reilly Media, 2026.