Why is it a "pool"? Shouldn't it be a "Dark Exchange"?

The Kraken dark pool is an order book not visible to the rest of the market. Each trader only knows
their own orders. Traders can anonymously place large buy or sell orders without revealing their interest
to other traders. Typically, outsized orders, when seen by other traders will cause the market to move
unfavorably, making it more difficult to fill the order at the desired price. This unfavorable price movement
may be avoided in a dark pool.[/b]