An end-to-end analytics platform offered as SaaS. It integrates Data Factory, Data Engineering, Data Warehouse, Data Science, Real-Time Intelligence, Databases, and Power BI on top of the same storage, OneLake.
In DP-900 it is in the large-scale analytics outline alongside Azure Databricks. Microsoft focuses new analytics investment on Fabric; Azure Synapse Analytics is still available, and there is guidance to migrate to Fabric.
Microsoft Fabric is a concept that can show up on the exam. Check the full guide to see it in context.