BBC business editor Robert Peston with a new acronym
You may feel that there is quite enough in the way of acronyms and jargon in your life, but I'm afraid to say that I have to introduce you to the concept of the G-SIFI - which would be centre stage at the G20 meeting in Seoul if trade imbalances and flows of hot money from the US to China weren't a source of some cattiness between world leaders.
There has been an outline agreement at Seoul on what to do about those supposedly dangerous G-SIFIs, following a recommendation by the supreme decision-making body of central bankers and regulators - the one that sits above the Basel Committee on Banking Supervision - the Financial Stability Board.
G-SIFIs are "global systemically important financial institutions". They are, to quote the FSB (no, not Russia's internal security agency; wake up!), "firms whose disorderly failure, because of their size, complexity and systemic interconnectedness, would cause significant disruption to the wider financial system and economic activity".
Now as luck would have it, the UK boasts more G-SIFIs relative to the size of the UK economy than any other G20 country.
HSBC, Barclays and Royal Bank of Scotland, all of which have assets and liabilities greater than £1.5 trillion (rather bigger than the UK's GDP) and all of which have investment banking, commercial banking and retail banking operations in many countries, are all indubitably G-SIFIs.
Standard Chartered, which is a good deal smaller in respect of assets and liabilities (if not in market value), may be a G-SIFI, because it is so international.
Lloyds, which is a very UK-focussed bank, is probably just a SIFI, rather than a G-SIFI. If it went kaput tomorrow, it could wreck the British economy - but the damage to other economies would probably be indirect (via a potential loss of confidence in other banks) rather than direct.
The big thing about these G-SIFIs, apart from their sheer size and complexity, is that they are supra-national institutions, at a time when the supervision or policing of banks, and insolvency procedures, remain largely national affairs.
This is a recipe for mayhem in markets and economies, were a G-SIFI to go down - which is what we saw in the autumn of 2008, when Lehman Bros died. And it's as well to remember that compared with an RBS or a Barclays, Lehman wasn't a particularly complicated G-SIFI.
That's why, when other G-SIFIs got into serious trouble after the Lehman debacle, none was permitted to go bust: RBS in the UK, Citigroup in the US, UBS in Switzerland, as only the most egregious examples among many, all were bailed out at huge expense by taxpayers.
Or to put it another way, capitalism failed - because those who owned the shares and subordinated debt in these banks, and were rewarded during the good years for the risks being run by these banks, did not pay the appropriate price when the risks went bad.
So what the G20 leaders have endorsed is the outline of a plan that should end the madness of these G-SIFIs and their owners being allowed to do what they like, safe in the knowledge that they're protected by taxpayers if it all goes horribly wrong.
Execution of the plan, however, will be fraught with difficulties.
It requires regulators and supervisors from Beijing to Moscow to London to Washington being equally expert, and intrusive and robust in their dealings with the likes of Goldman Sachs, Deutsche Bank and BNP Paribas.
It requires every major country in the world to harmonise special insolvency or resolutions procedures for banks - which will entail heroic attempts by parliaments in many countries to streamline new bankruptcy laws.
It requires governments and regulators in every major country in the world to legislate so that a massively higher proportion of the liabilities of these G-SIFIs can be converted into loss-absorbing equity in a crisis - and it requires investors to supply these potentially loss-absorbing loans and additional equity without massively increasing the funding costs for banks, which could raise the cost of borrowing for households and businesses.
On this last point, here's an illustration of the scale of the financial challenge. Work by the FSA and Bank of England suggests that perhaps a third of the balance sheets of G-SIFI has to be loss absorbing in the form of pure equity, contingent convertible bonds (CoCos) or bail-in debt, in order to sufficiently shield taxpayers from risks.
That compares with a ratio of core equity to risk-weighted assets of just 7% for smaller, simpler banks, under the new Basel lll rules.
So even if the G-SIFIs are allowed to calculate their assets on a risk-weighted basis when assessing their loss-absorbing needs, it would require the likes of Barclays, RBS and HSBC to raise many tens of billions of pounds of loss-absorbing capital - which will not be cheap or easy for them to do, and which they wouldn't have to do if they weren't G-SIFIs.
Here's what I think is really gripping about the G20 agreement on G-SIFIs: it sets a huge challenge for the boards of G-SIFIs and the owners of G-SIFIs in respect of determining whether the putative financial benefits of being a huge complex international organisation outweigh the new additional costs being imposed on them.
If the G20 countries follow through on their G-SIFI pact, one rational response by the G-SIFIs could be to break themselves up into smaller simpler organisations, to avoid the new capital requirements and the regulatory intrusiveness that will be the other price of being a G-SIFI.
All of which is likely to put the share prices of G-SIFIs under a black cloud for some time, until the precise new cost of remaining a G-SIFI is quantified.
But if you're starting to feel sorry for the G-SIFIs, here's a remedy.
The chairman of a G-SIFI recently confided in me that he could live to be a hundred, and he still wouldn't have a grip on all the risky things that his massive bank does in the nooks and crannies of the financial world.
If he has recently come to the view that his bank and its shareholders would be better off if it was a slimmer, simpler organisation, then it would probably be foolish for governments and regulators to weaken in their resolve to disarm (so to speak) institutions like his that they see as weapons of mass economic destruction.
PS: There is one group of firms which should probably be even more alarmed by today's G20 agreement than the G-SIFIs. They are the credit rating agencies.
Because the G20 leaders have agreed that central banks and regulators should strive - wherever possible - to cease using their formal ratings of debt and institutions in assessing the riskiness of that debt and those institutions.
Bang goes the rating agencies' monopolistic business model.
You can keep up with the latest from business editor Robert Peston by visiting his blog on the BBC News website.