Louis Davidson does some exploring:
Clustering is one of the data terms that could not have been created by a database design person. Why? Because it has multiple meanings. In PostgreSQL it means the same thing as an instance in SQL Server. In server architecture it means connecting multiple servers together to form a “single” unit of some form to protect against failure. Then it means an index that determines the physical storage of a table in some manner. This usage of the word means the former.
The weirdest part of using a Fabric Data Warehouse when you first try to look at a query is the lack of indexes. So (currently as of writing this is late 2026), you only have this one tool to affect your performance. The tool allows you to order the data physically in your files so query processing can be reduced when searching the physical file.
Read on for an introduction of how it works, with the caveat that Louis is about two pages ahead of most people in the book.