What is it and the whole thing revolving around it? A bit of history, how it will change user experience and the benefits? Please explain in layman's term.
Here it is in a nutshell, I may have oversimplified in some places so those who know more than me don't pounce too quickly!
So there are two major processor types in consumer electronics.
x86 and ARM. Think of them as two different "languages" for say, the software to speak to the processor.
x86 has it's roots in desktop computing, based around performance and functionality. Suitable for a desktop computer which was plugged in anyways.
ARM had its roots in mobile, which meant an emphasis on efficiency over performance. Suitable for PDAs and phones which had batteries to worry about and had smaller, simpler software.
The two are inherently incompatible, sending ARM instructions to an x86 processor won't work. And vice versa. Like two people speaking Spanish and Vietnamese. We would see it with Windows RT, which was, for the most part, Windows 8.x retranslated to speak ARM instead of x86. However, this meant that most legacy applications built for x86 Windows would not run as they have not been translated.
(and the translation is something that requires source code to do, which meant for many well-known pieces of software, it would require the developer to translate their program. MS decided it would be too complex and made it so RT would only run Store apps. But jailbroken RT could run some rebuilt programs.)
Anyways enough of that tangent. With enough processing power, one can make software that translates between the two, like emulation/virtualization. (like how there are apps/programs that can "pretend" to be a Gameboy Advance and run Gameboy Advance games while the underlying hardware is very much NOT like a GBA.)
So with enough effort, one can introduce an "interpreter" to translate Spanish to Vietnamese and vice versa, but it introduces performance overhead. On an x86 computer, it was powerful enough anyway and power wasn't as big of a concern so we had Android, iOS, etc. emulators for development and such.
But it was impractical to try to have an emulator shoehorn desktop Windows to run on a relatively weak ARM chip. It would be like having an interpreter translating, except that interpreter only had two weeks of Vietnamese lessons and was only given a rudimentary Spanish/Viet dictionary. It would not be pretty. Which made the announcement a bit of a surprise for me.
Anyways, here's some more context:
ARM chips run a whole lot cooler and efficiently than x86 chips. Fans for cooling were a given on desktops, laptops, etc. But phones and tablets built on ARM didn't need fans. Like how the Surface RT was fanless yet the Surface Pro had a fan. (although the x86 Pro was much more powerful too, you could run Crysis on a high-end PC, but on a phone? well...)
Intel made significant strides with a fanless x86 chip (recent Atom generations saw x86 in fanless tablets, a couple phones) but it wasn't quite as competitive. Eventually they stopped.
So right now we have ARM chips working to get more powerful (worth noting that system requirements have largely leveled out in the past decade since Vista launched) and not doing badly at all.
x86 chips have gotten a lot cooler and more efficient, but right now ARM still has the upper-hand in mobile applications. And with Intel canceling their line of lower-cost, lower-power Atom chips some time ago, it created a sort of void in the market that MS is filling with software instead of waiting for someone to enter with hardware.
As announced, much to the surprise of many, Windows 10 on ARM is full desktop x86 Windows retooled to run on ARM chips. Except apparently there is a translator so that legacy x86 programs run at an acceptable performance level. Which surprised me, since I still considered it infeasible from a performance standpoint.
What does this mean for the consumer?
In the next couple years, assuming Windows on ARM doesn't faceplant or fade into the night, we can likely expect tablets and maybe laptops with ARM chips running full Windows 10 to appear, complete with the power efficiency and thermal benefits ARM brings. Back when Intel still had the Atom chip, we saw a lot of 8" full Windows-tablets running around that aren't quite around anymore. Maybe we'll see a lot of small form-factor, lower-cost PCs.
As for phones, it's a possibility since hey, phones! But that's going to be a while, at least a couple years of work. Desktop Windows is a large beast with requirements that outstrip iOS and Android and while it will fit well on a tablet or laptop as we've seen, making it fit on a much smaller phone will be a difficult task, both hardware requirements-wise and user-experience-wise.
Seems to me Microsoft has forgotten they already have a product running ARM processor......
Windows 8/8.1 RT.... hello !
How about taking care of that first ?
Unfortunately the RT is long left behind, although I remember the intense speculation over whether it will see Windows 10 or not. At least we still have security updates though.