(1) Topographically speaking, a bluff is a steep rise with a rounded face and flat top. Similar to but smaller than an escarpment.
(2) Something to fall down. Also called promontory, riverbank, and cliff. Or hill. Often too steep to walk down without handholds or a switchback trail to help.
(3) A steep bank created by erosion by the action of a river or waves. A rocky area is often called a "cliff" while the equivalent, made of softer stuff is called a "bluff".
Bluffs are like escarpments that are only bluffing. Probably grassier, and you might find one on the edge of town, unlike a mountain range.
We walked out to the bluff overlooking the river and then Ed fell off. We thought he was only bluffing. Maybe he was.