what does slippage mean to you?

Answer 1

slippage is the market terms for the difference between the price you think you're going to pay for the shares, futures, options, or contracts you order and the price you actually get.

In the time between your decision and the execution of your order, the market moves. Slippage is the amount of that movement, usually expressed in percentage of the price you thought you would get.

It applies to both opening a position and closing one (with minor exception for derivatives exercised).