What's the difference?

[Nikonoff]

AF-P won't work with your D90!

Like John says, it's the way(or type of) focus motor system in the lens.

The last issue with the consumer dx model lenses is if they are VR models too. I don't think any of the Dx VR lenses have a VR on off switch!
Not only is this the second stupidest design choice of all time ... ever, it adds to the compatibility list above.
That is, you can't turn VR off if you don't have a camera that is fully compatible. The option to turn VR on/off is now an in camera item, not on lens like the old days.
I think the firmware update for those listed cameras adds the VR option in the camera menu.
The Fx version of the 70-300 f/4.5-5.6 VR does have the VR on off switch, so isn't affected in this way.

Arthur a simple thanks seems grossly inadequate, but I can't think of a clever superlative, so thanks for the very interesting and informative read.
Regarding the DX lenses with VR they do indeed have on/off switches, when I bought mine it came as a twin lens kit, both DX VR. I find the 18 - 55 to be particularly good for a budget lens and since my daughter sort of claimed it I find myself looking to acquire another one hence the initial query. Thanks for clarifying Arthur, I'm going to copy/paste you reply into a word doc for future reference.

[arthurking83]

.....
Regarding the DX lenses with VR they do indeed have on/off switches ....

You've misread my comment.
These new AF-P Dx lenses, don't have the VR on off switch.
Up until those new ones, you're right they do have them, and all VR lenses Nikon have made had them.
This is another change that Nikon has stuffed up..
With these VR AF-P lenses without the VR switch, you can only turn the VR on/off via the camera's menu.

The only AF-P lens with VR that has the lens switch is the non Dx 70-300 AF-P f/4.5-5.6 lens model.

Can't help but think .. are Nikon so hard up for profitability that they really need to save a few cents on a couple of hundred dollar lens product? Just add a little extra for the switch which they do for the VR mechanisms anyhow!

So this is why some cameras aren't fully compatible with those new lens types either. And others are fully compatible with a firmware upgrade too. The firmware adds the VR on/off item in the camera menu.
I think there are a few cameras that are affected in this manner, and when updating the firmware subsequently become fully compatible.

Hope that clears up the misunderstanding.