Polybase is a data virtualization feature for SQL Server
Allows SQL Server to query data directly with T-SQL from multiple databases (Oracle, Teradata, MongoDB, Cosmos DB, Hadoop Cluster)
Allows to join data from SQL Server with external data
INFO
Polybase has 1 MB row size limit when working with Azure Synapse and 32kb when working with Azure SQL Server
The fastest and most scalable way to load data into Synapse is by using Polybase
It also allow to access data in Blob and ADLS using T-SQL
Design a PolyBase data loading strategy for Azure Synapse Analytics | Microsoft Docs