By engineers, yes.
Way back when we were safeguarded by bold acronyms like NATO and NORAD, when the world being baptized in nuclear fire was a real worry, engineers in the aerospace industry took to referring to titanium as 'unobtainium'. It was ideal for a lot of applications because of its high strength and light weight, but it was unavailable as well. The best sources, if not the only sources, were in the Russian Bear's territory.

: and essentially now used by any writer who
: wants to employ some element

Heh. Neither of the Unobtainium materials in The Core and Avatar were elements.

: that doesn't (yet?) exist on the periodic
: table to accomplish a task no element that exists on the periodic table
: can perform. Whether believably similar to an existing element or not,

You could also complain about how Quantum was appropriated by Star Trek to mean "Whatever the #$% we want it to".

I really prefer my definitions of unobtainium/handwavium, because there ought to be something that differentiates hard science fiction technology (We've crunched the numbers, thought about how society would use this material, and did our homework) and soft science fiction technology (It's an alloy that can withstand the temperatures of solar flares and blocks psionic waves)

: IMO: space magic. :P

Just out of curiosity, but was I the only one who looked at the Unobtanium in Avatar, saw it floating on a metal base, and realized that it was a room-temperature superconductor?

: Hard light was in Halo 1 for bridges, though I've seen the
: discussions/debates about its implementation and what it actually was/may
: be.

It's a completely different beast in Halo 4.
The Hardlight we saw in Bungie's Forerunner structures looked like primitive holograms or glowing force fields. 343i's interpretation is stuff-that-is-indistinguishable-from-real-matter-until-we-need-it-to-do-something. And, you know, it's only ever used in a handful of disparate applications, rather than wherever it would make sense to implement it.

: Taken on the surface - this is a game element on which 343 seems to be
: basing its hardlight uses. Love it or hate it or debate it. The concept of
: 'hard light' existed, on the surface, before 343 took the reigns.

Just like how John's armor or the Forward Unto Dawn existed before 343i took the reigns.

: They're
: just running with it, and saturating the environments with it. Love it or
: hate it. Still space magic :P

Saturating the environment with it? Hardly.
It's used in a few gimmicky applications, but it's limited to the plot convenient locations and the stuff that 343i didn't want to create unique destruction animations for.

: Yep. Some love it, some hate it. :)

Generally, it's a sign of the author having no clue what he's doing.

: I differentiate biological from mechanical purely in that line between
: "running" by a means we are able to accomplish
: (manufacture/construct material; flip a switch), versus not (we cannot
: give that 'spark of life' to the molecules, which we could assemble, in
: order to make it "run"). Beyond that fundamental step, humans
: and robots are machines. Theoretically (ie via space magic), we could
: 'construct' a human by coordinating molecules (eg Tron or Star Trek
: transportation), but somehow we'd need to recreate that 'spark' of life.
: Tron/ST presume that the reconstruction somehow includes that 'spark' to
: make the reconstituted biological machine (continue to) tick.

Meh.
I strongly dislike the 'spark of life' trope for a number of reasons. Namely, it's overused and smacks of 'humans are special', and because I believe in something similar IRL (It's complicated), I like to read fiction that doesn't mirror real life.

If you could duplicate someone atom-for-atom, I have no problem believing that the result would a moving, breathing, living duplicate indistinguishable from the original.

: This is one reason I absolutely love the Halo AI, because it deals with what
: some entity alive; Cortana being a (space magic'd) duplicate of Halsey's
: brain. She has personality, intelligence, capabilities that match Halsey,
: but without biological limitation, only technological. Is Cortana alive?
: Is she just a program running code (which btw wasn't hand-coded, but
: machine generated based on a template, the cognitive impression modeling
: process). Cortana isn't a biological machine, but is she alive?

She has agency, therefore she is alive.
In my opinion, that's pretty easy to answer. Halo does many things well, but one of the things that it rarely does well is artificial intelligence. AIs are mostly just holographic humans. Until Halo 4, Rampancy was all talk, particularly in The Cole Protocol.

Want a real challenge? Consider artificial intelligences that don't think the way we do, that don't represent themselves with human avatars. Is Vergil alive? Is it a sentient entity with a limited ability to communicate its thoughts, or is it just a chatterbox that can execute high-level directives?

: (that's
: rhetorical :P)

Duly ignored. ; )

: Where do you draw the line?

Are the user's arms and legs encased in the machine's arms and legs? If yes, then it's power armor.
If the unit is big enough to encase the entire person inside the body, then it's a mech.

There's a certain gray area, in that Terran Marines/Firebats/Marauders are too big for the person's arms to be inside the suit's arms like we've seen. But mostly, I feel comfortable with the system I outlined.

: If you defined power armour as say a wearable
: machine that enhances your capabilities without hindering your normal
: actions, then I'd say yeah that's different than a mech.

Precisely.

: I'd say a mech is
: a wearable machine which is more akin to the human being the pilot, than
: parts of the human being enhanced by a frame. The question is where is the
: line between those classifications?

Power armor is something you wear, a mech is something that you're strapped into. See above for more info.

: A mech (humanoid, based on what I'm
: arguing) IS an enhancement of human capability; it's a large machine that
: mimicks to some degree the construction of the human biped, but built and
: augmented with various levels of accessories, designed for specific tasks.

In the same way that a vehicle enhances a person's mobility, yes.

: A chainsaw isn't power armour. It's not a vehicular tool.

I was shooting down your argument, that power armor and mecha would share much of the same technology.

: and it could become a part of power armour :P

: Seems we're debating
: whether that limit is here, there, a defined range, or a blurry region.

Blurry range, I guess, though the border sometimes narrows down to a thin red/blue/green line.

: To bring it back, Halo 4 has moved much further
: into Space Magic territory than Halo 1 was. And has introduced much more
: fantastical (fantasy-like) content than Halo 1 had.

One of the reasons I dislike it. Especially how the Forerunner seem less mythic, and more fantastic.

: Space magic!

Eh. Just watched Pacific Rim for the first time. Felt like an entire season of anime crammed into two hours.

7/10, won't watch again if I'm sober.