It's our new high-performance runtime, using a native vectorized engine developed in C++.
Please see our blog for a great overview.
https://databricks.com/blog/2021/06/17/announcing-photon-public-preview-the-next-generation-query-en...
Databricks SQL uses Photon by default. (You can turn it off)
Databricks DE/DS has an option to choose Photon as an engine for your compute intensive workloads.