Microsoft has decided that all new PC keyboards should be equipped with a new key for the first time since 1994 when the Windows "Start" key was added.
For those that have been paying attention to what Microsoft is currently pushing very heavily, it won't come as a huge surprise that this new key will be a "Copilot" button which will instantly launch their AI assistant side panel. This should work on any up to date Windows 10 or 11 PC (unless it has been deliberately disabled for some reason, in which case it will open the search menu).
Where will the key go? It will depend on the keyboard. It may replace the button to the left of the right hand Ctrl key - sometimes called the "Menu" key, although its function can sometimes vary, It may also appear between the arrow keys and the right hand Alt. There's not a strict command on where exactly it should go, but it's very likely to be in that area of the keyboard in most, if not all cases.
As to when you may see this new key in the wild, it seems certain that it will come to Microsoft's Surface range of devices sooner rather than later and Dell have already announced that this year's XPS laptops will include it. Microsoft have hinted that they will eventually require all major PC manufacturers that they work with to include it.
The significance of this is not really the key itself - there's already multiple ways to open CoPilot (including Win + C if you want to use a keyboard shortcut). It's more an indicator that Microsoft is so sure that Copilot is going to be an integral part of Windows for years to come that they're mandating that new Windows-compatible hardware be altered to include it. This is not something you'd do if you were at all unsure of its staying power. There was never a Cortana key, for instance...