What is UPnP & Why is it Dangerous?

Thanks Adrian, that’s interesting and helpful.
So, if I’ve understood it correctly, introducing an UPnP streamer to my system and router shouldn’t in itself pose a security risk.

This comment from Simon…

I have Virgin media router, how would I disable UPnP at the router or know whether or not its disabled?
How do I a check for UPnP updates applied by my router as suggested by @Simon-in-Suffolk
In very lay terms if you could please, would be appreciated.
Thanks