It's the opposite of "factoring", hence the name.

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Note added at 31 mins (2010-11-03 20:12:51 GMT)
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El confirming equivale a un
pago certificado, con la
diferencia de que aquí el banco
avala el pago al proveedor. De
hecho, es un factoring inverso ya que lo inicia el cliente y no el
proveedor. En consecuencia,
en inglés este servicio se llama
Reverse Factoring (y no, como
uno podría pensar, Confirming)

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Note added at 17 hrs (2010-11-04 13:22:40 GMT)
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I really didn't imagine this would require further explanation but if Richard B. insists.....After all, does it not surprise anyone that in the original Spanish they should suddenly "lapse" into English as if Spanish didn't already have a verb, "CONFIRMAR". Or perhaps no-one noticed.......

It's one of the most common services offered by banks here and abroad to the Self-employed, SMEs, larger companies etc...

Barclays explains it better than I could:

Barclays Confirming (Reverse Factoring)
Barclays NOT JUST ANY Current Account.

An integrated management service for payment to suppliers in which Barclays Factoring (Barclays Group) manages the payments that your company has to make to its suppliers, also offering them the possibility of receiving an advance on their collections.
Advantages of this Service:

FOR YOUR COMPANY:

* Your supplier relations will be improved.
* Your administrative processes will be simplified.
* You will reduce costs by avoiding stamp duty on financial instruments and the costs relating to banking operating procedures.
* You will be able to obtain extra financing on the whole of the debt, deferring payment of invoices without having to agree this individually with each supplier
* You will be able to place your cash flow surpluses, and may at any time make advance payments of invoices, obtaining discounts for prompt payment.
* You will have the possibility of carrying out self-billing, allowing you complete control of the accounts of your suppliers and additional tax advantages.

FOR YOUR SUPPLIERS:

* The possibility of immediate collection of their receivables.
* Obtaining a new financing facility quickly and easily.
* An increase in borrowing capacity, as advances do not increase bank exposure and the amounts advanced can also be eliminated from their balance sheet.
* Cost saving: the costs relating to stamp duty, the collection of instruments and the possible involvement of a public certifying officer.

Adjustment of their cash flow: we offer all the various options, advancing the total amount or withholding the document until they require liquidity or it becomes due.

* Simplified administration.
* Internet enquiry from the private web page of Barclays Supplier Confirming (Reverse Factoring) of the status of their invoices, allowing them to request advance payment of these invoices.

In addition to the technical resources, we are also continually focusing our efforts on the personalised and preferential service required by suppliers, so that a change in the way that they receive their payments, far from being a complex process for them, is turned into a real advantage.

https://www.barclays.es/publico/contents/empresas
/cobrospagos_BarclaysConfirming.jsp?lang=en_UK