As of release 138 the SILVA databases, its taxonomy, and all files provided for download are licensed unter Create Commons Attribution 4.0 (CC-BY 4.0).
All data is freely available for academic and commercial use as long as SILVA is credited as original author and a link to the full license is provided.
Releases before SILVA 138 are not affected by the new license. Please refer to the license file provided in each download directory for the license associated with the provided files.