No ... they are not the same. When the market is 47.25 x 47.50 the tic is spread. When you execute an at the market buy into that .25 x .50 market and you don't get your fill at .50 (or a better example is when I have a buy stop @.50 -- which becomes a market order -- but get filled @.75 or even 48.00) the extra tic or two is slippage.
None of this (particularly two tics of slippage) is common in ES but, as an example, is quite common in CL. Keep in mind just before you get executed for your one, five or twently lot a player could sweep 400 offered and still not complete his 500 lot order. It happens and it even happens on occasion during RTH. Again, it is not common. ES is one of the few markets where you can execute market orders with little to no concern of slippage. The overwhelmingly high percentage of your trades will execute at zero slippage.
None of this (particularly two tics of slippage) is common in ES but, as an example, is quite common in CL. Keep in mind just before you get executed for your one, five or twently lot a player could sweep 400 offered and still not complete his 500 lot order. It happens and it even happens on occasion during RTH. Again, it is not common. ES is one of the few markets where you can execute market orders with little to no concern of slippage. The overwhelmingly high percentage of your trades will execute at zero slippage.
Quote from QuantWizard:
Spread is always 1 tic with ES, so in this case they are the same.