I have read definitions for both "slippage" and "spread" on Investopedia, but still do not understand it. I think spread is very complicated. But perhaps I do understand what slippage means. My understanding of slippage is: when I place a market order for 1 contract in hopes of getting filled at, say, 1500, the market order actually fills at 1501. This is slippage? If so, it seems slippage happens each and every time I place a market order for an ES contract. It never gets filled where I want it to. On the other hand, I have given up (almost) on understanding "spread". It seems to be a very complicated concept which I am still a long ways off from grasping.