What is the deal with Pumpkin Spice Lattes?

As the revolution of the Earth starts pointing the Northern Hemisphere away from the Sun, Americans start talking about something called Pumpkin Spice Lattes (and their variants). As I am Australian and Mormon, could somebody please explain to me what this is? I admit bemusement, especially as sooo many of you seem annually addicted to it.

Now, I know what pumpkin pie is, having lived in the States for some time, but I left long before lattes became A Thing, ne'ermind pumpkin spice lattes, or even before Starbucks reached Utah. (I find it ironic that the HQ for Starbucks in Seattle is located on a street called "Utah Avenue".)

So... my best guess is that it's a pumpkin-flavoured (?!) milky coffee with a combination of spices such as nutmeg, cinnamon, ginger, and cloves as one might use in a pumpkin pie.  Now, spiced coffee has been around for a Very Long Time, and Chai tea for the same amount of time. I'm just wondering who thought, "Hey, let's throw some pumpkin into our coffee and see who'll drink it."

I have had spiced pumpkin-flavoured milkshakes in Utah several decades ago, so a pumpkin-flavoured drinks isn't a new idea, but pumpkin-flavoured coffee?

Yeeaaah--Nah.

Now, if it isn't pumpkin flavoured, why is it called "pumpkin spice latte"?  Why not just call it a spice latte?

Much 'splaining to be had, pleeze?

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Australians don't do the pumpkin spice latte thing, either because it's not culturally connected, or they consider it a ridiculous idea, or they call it by a completely different name.  Also, there are no Starbucks in Western Australia.