What is the slippery slope fallacy?

Claiming one small step must inevitably lead to an extreme outcome, without showing why the chain of intervening steps can't be stopped.

Also called "the camel's nose." The pattern: "If we allow X, then inevitably Y (something drastic) will follow." It's fallacious when no argument is given for the inevitability — there are usually many steps between X and Y, and no reason is offered why each will unstoppably trigger the next.

"If we let students retake one exam, soon they'll demand to retake everything, then grades will mean nothing, and the whole degree will be worthless."

Each link is asserted, not justified. A slope isn't always fallacious — if you can give real evidence that one step reliably causes the next, the reasoning is legitimate. The fallacy is the bare assertion of an inevitable cascade.

Tip: Ask "what forces each step to follow the previous one?" If the answer is just "it would," the slope is greased with fear, not logic.