I am a grumpy old cat. At risk of catching it from Burakkucat. I rather hate the word dual-stack because I think it’s horribly overused. As best I can make out it arose from o/s designers who were designing o/s TCP/IP subsystems that had support for both IPv4 and IPv6 in an integrated fashion, as opposed to IPv6 being an independent add-on like a driver for a new and completely alien protocol.
When Microsoft spent ages on the new TCP/IP networking subsystem for Windows Vista, which kept getting delayed further and further for whatever reasons, then they had the opportunity to do IP right and it seems completely rewrote parts of the IPv4 stuff so that it used common code from the IPv6 side of things, and that caused IPv4 behavioural changes that were real improvements. (It’s been too long ago now, but I read Microsoft’s book about IPv6, IPv4 and Vista.) For example the source address selection algorithm was made available to IPv4 not just IPv6.
So that was an example of ‘dual stack’ being used properly, about a style of operating system design. And to me that was _the_ correct kind of usage. But later people, understandably, started using the word just to mean something really vague like ‘I have IPv6 and IPv4’ which is already so vague that we can’t understand it - what is it that they do they ‘have’? If it means that they have an o/s that is capable of speaking both IPv4 and IPv6 - then that is every modern o/s, so it’s not saying much.
So I like clarity. Things that are simple to understand.