30 Second Terminology
When a player Slips, commonly known as a "Slip Screen" or "Slip Cut" is when a player sees that the defensive has left their assignment and looks to take a quick angle towards the basket. Often when an offensive player goes to set a screen their defensive player will help the man getting screened by hedging the screen. This forces the offensive player back towards their own defender. In this case, with both defensive players committed to the ball handler the screener can "slip" away towards the basket for either an easy basket themselves or to draw away help side rotation creating shot opportunities.
A Slip Screen can also be utilized when an offensive player quickly sets up in a screening position but instead of holding the screen quickly flashes to the basket. It's a move that can often catch defenders who are anticipating the screening situation off guard.
Below is an example of the Houston Rockets using slip screens in a pick and roll situation to create shot opportunities.