This fallacy is so common that it has become a cliché: "Give 'em an inch, and they'll take a mile." 

It occurs when one makes the assumption that, because one concession is given, a "slippery slope" will be created that allows more extreme concessions to follow. Once you start slipping, you just keep on slipping further. This logic is faulty because it ignores the fact that, at any time, one could simply say: "Nope. No more concessions. That's it." 

The slippery slope fallacy is similar to a faulty extrapolation because it makes a prediction, but they differ in a couple of key ways: 

1. Faulty extrapolations use statistics to make their predictions whereas Slippery Slope fallacies do not.

2. Faulty extrapolations simply jump to future predictions while Slippery Slope fallacies detail the multiple steps needed to get to those future predictions.

The Slippery Slope fallacy is sometimes called the "Domino Effect Fallacy" (self explanatory) or the "Camel's Nose Fallacy," which satirizes the logic that, If you let your camel stick its nose in your yurt one night, its entire head will be in there the next, and it'll be sleeping on your mattress before you know it. This is a fallacy because there is no reason to believe that, by letting its nose in the  yurt, it will eventually be sleeping in your bed forcing you outside. All you have to do is draw the line and make it sleep outside the next day. Any further concessions to the camel would be your own fault. But, hey, you do you, you know?