Investment - Market Structures - Order  Driven Markets 
Order Matching: Order-driven markets use rules to match buy and sell orders in order to arrange deals. Usually, the orders include the quantity that the traders wish to purchase or sell, as well as possible price details like the highest amount the buyer is willing to pay or the lowest amount the seller will take.

Algorithms are now largely used by computers to conduct the matching.

Trades are frequently made between strangers because rules match buyers and sellers. Order-driven markets, meanwhile, are dependent on settlement mechanisms to guarantee that buyers and sellers fulfill their trading obligations and complete their security deals.   

Otherwise, if a shift in the market made settlement unprofitable, dishonest traders would not fulfill their obligations.