Tankbusters?

I am asking what exactly is a Tankbuster. I Paladin tanked mainly hard mode Primal fights (for the MSQ and Relic), dungeons and the occasional lower tier raid in ARR. Extreme Primal fights and the top end progression raid never interested me, so I never signed on to do them.

Long story short, I am leveling and enjoying Dark Knight and I keep reading about Tankbusters here on the forums. What exactly is it, and how does one know when one is coming?

I presume it's just a community-made term to refer to any extremely powerful, short range attack an enemy uses that particularly is hard to mitigate with defensive buffs - I've only started hearing the term myself so I'm just making assumptions here (I don't do endgame so I might not be the best one to provide advice on this subject however. :p).

It's a term mainly relevant in Coils and other 8 man raids.
Bosses have attacks on varying cooldowns that will kill you if you don't mitigate through them.
These are called tank busters because they're attacks designed to bust tanks.

The majority of tank busters (or "tank crunches") have visible cast times, so it's reasonably easy to tell when one is coming. I usually see the term applied to attacks that deal a high amount of damage even if they don't outright kill the tank, however. Titan HM's Mountain Buster ("Table Flip") is an example of one of these types of tank busters: it deals a hefty amount of damage, and is survivable without cooldowns, but it's really helpful if you use one during it.

It's a single or multi-hit attack that does well over the HP of tanks in damage. unmitigated, it will kill you, and hits hard even when mitigated.

some examples of this are Death scentence from turn 5, mountain buster from titan HM and EX, raven's beak from turn 9, flatten and Akh morn from turn 13, perpetual ray from Alex, and an unsplit blinding blade from ravana EX.

I'd define it as:
an untypically high-damaging and unavoidable enemy ability or ability+mechanic within an encounter that was specifically designed to put the tank at risk of being killed.

I like to think of it as a reason to bring tank rather than just having a DPS do the tanking. In Titan HM after heart phase, every landslide Titan does is followed by a Tank Buster called Mountain Buster--Back when I was in Darklight and Mythology this would bring me to about 10% HP after being mitigated with a buff. Now DRGs can tank it pretty comfortably though

Who you gonna call? TANKBUSTERS!

From what i gather a tankbuster is a hard hitting move that ideally only the tank should receive.
In most situations a tank buster will kill a non-tank, and deal heavy damage to a tank even with mitigation.
Some tank busters come with debuffs that reduce defense or hp, requiring the use of another tank via "tank swap" while the first recovers from the debuff.

The differece between a tank buster and a cleave is the need to mitigate damage. Some tank busters cleave, but not all cleaves deal the damage and debuffs to inconvienience the tank.

Examples of tank busters:
Mountain buster from titan hm and ex
Disease breath from AK normal boss.
Bahamut's claw and Ravensbeak from T9
Akh morn from t13

If it has the power to one-shot you even when you're at full health, then it's a tankbuster. It's like the boss stress-testing you as a tank -- gear check, hp check, skill check (as in, what cooldowns do you use on it, what rotation do you use to mitigate each tankbuster so that you always have something up for it, etc).

Example, in Alexander - Fist of the Father Savage, the tankbuster is a move called Hypercompressed Plasma. Each Oppressor casts it against its tank. It WILL obliterate you unless you use serious cooldowns (unmitigated, it hits for over 20,000 HP).