> The documentation says on Classic and SuperClassic allow simultaneous connections to a database. What is that?

Which documentation? Do you a link?

> If I have 8 computers concurrently opening 4 databases on a Firebird server, how many simultaneous connections is that?
>
> If I have two more applications on each of those 8 computers opening 2 of the same databases, is that counted as more simultaneous connections?

Don't worry about that. Firebird is a client/server DBMS with one
dedicated process for SuperServer and SuperClassic per "instance" and
one process per database connection in Classic.

Even the Embedded Engine, although running in the same address space
than the client application, allows multiple attachments to the same
database across several embedded in-process instances or regular
Classic/SuperClassic server instances. Firebird bitness (32-bit/64-bit)
must match in that scenario though.

Regards,
Thomas