It is most likely in the "Additional Use Grant" which is tricky - because this additional use grant is distinct to each product licensed under the BSL. This additional use grant is also not that easy to find, since some licenses display it prominently, and others hide it under some additional legal fineprint[1,2].

From mariadb site: https://mariadb.com/bsl-faq-adopting/#limits

"Q: What are the usage limitations under BSL?

A: The usage is limited to non-production use, or production use within the limits of the “Additional Use Grant” defined by the vendor using BSL and specific to each BSL product."

[1] obvious Additional Use Grant for Couchbase, included clearly in https://blog.couchbase.com/couchbase-adopts-bsl-license/

[2] it is extremely difficult to find the Additional Use Grant for Mariadb products themselves. For MaxScale, which is their proxy product, it is buried in a file within the source code (which on the surface level might be a good place for it, but it's not very easy to find and I had to go through lots of legal print to get to it) : https://github.com/mariadb-corporation/MaxScale/blob/2.5/LIC... or https://github.com/mariadb-corporation/MaxScale/blob/6.3/LIC... depending on which version you are trying to use, etc.

I wasn't referring to the BSL specifically with that comment, I was referring to recent attempts to call licenses like the Hippocratic License "open source" despite being anything but. The BSL is just a different example of a similar thing.