I don't think I can do better than quote from the previous discussion of this in October 2007, so with your indulgence, I'll copy my reply from that time (some of which is quoted from other GPL-related documents), and please feel free to comment if you have a different interpretation of the GPL. Any explanation here is of course without prejudice to actual licence terms. This is what I wrote in 2007:
Thanks for your interest. VOSS is offered under dual licensing, GPL and/or Commercial. To clarify, without prejudice, the GPL as I
understand it, and which is the intention in the VOSS licence, distinguishes between end-use and distribution (propagation), and the
GPL "copyleft" requirement, that everything in the same application also be GPL, applies to distribution only.
Modifications to a distributed GPL module must themselves be GPL, and modules statically or dynamically linked into the same
executable must also be GPL, whether the linking is done before or after distribution.
Other software included in a product package, but which runs in a separate operating system process, invoking or invoked by a GPL
module and typically communicating via data streams, would not normally be subject to the GPL, nor does the GPL cross the boundary
between operating system and user space.
An application which includes GPL and non-GPL components may be freely used internally for application development and/or end-use,
including on a web server, though not if it is exported to run behind a client's firewall. The definition of "internally" would
probably include wholly-owned subsidiaries, but not sub-contractors. Legal advice may be necessary (IANAL and the Commercial licence
may be cheaper).
A negotiable Commercial licence, sometimes in any case a customer requirement, is available for VOSS as an alternative, avoiding the
GPL restrictions and including a support package.