ما معنى Delay cost, opportunity cost, VWAP slippage؟

For a parent order decided at price $P_d$, released at the arrival price $P_a$, filled for $Q$ of its target $X$ at average price $\bar P$, with the price $P_e$ at its end: the delay cost is $sQ(P_a - P_d)$, the execution cost $sQ(\bar P - P_a)$, the opportunity cost $s(X - Q)(P_e - P_d)$; with fees they add up to the implementation shortfall (chapter 19). The VWAP slippage is $s(\bar P - \mathrm{VWAP})$, the average price against the market’s volume-weighted average price over the order’s life.