It means only matched trades are transacted. In other words, if someone offers to sell 500K shares @ say .0025 and there are enough open bids to buy 500k shares @ .0025 the trade will go through. But, and this is what makes it so different and severely limits liquidity, the shares are traded directly between brokers and not through clearing (DTCC). It cuts out the use of market makers and their ability to fill an order by them selling short the stock to fill the order to keep from losing the order. In effect, it stops the issuance of "air shares" by MM's even though the majority of those air shares may be covered within the required time frame.
This is the simplest way my simple mind has of explaining it.
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