Imagine that another desk within your firm sends a manual market order to buy 1,000 contracts of EDM9 when the visible liquidity is 1,000 @ 97.85. Suppose you could see this order before it was sent to the exchange and that you had some signal that predicted $\delta_{t,t+h} p_{t}<0$ (or an associated strategy that would execute at an expected average lower price).
What should you do? If your signal is high-confidence, you could "intercept" the order by filling the desk's order intended for the exchange at the visible price, and then covering your position later at time $t+h$ at the more favorable price. If your signal turns out to be accurate, then both books benefit: the former gets their order filled at the intended size and price with no slippage or other transaction costs such as market impact and leaking information to the market, and the latter pockets the price change $\delta_{t,t+h}p_{t}$.
If your signal turns out to be incorrect, then the desk at least gets the benefit of perfect execution, even if it as at the expense of your strategy, this being the accepted risk of running the strategy.
This type of strategy of intercepting aggressive orders, filling them immediately internally, and delaying routing to the actual order to the market or otherwise implementing some execution strategy is known as internalization and is an example of an opportunistic signal-driven algorithmic execution strategy.
