A Revenant is a corporeal ghost or zombie-like creature from folklore that was said to return from the grave to exact revenge upon the living or simply to terrorise people - in the original medieval tales Revenants often returned from the grave simply to cause trouble for the living and could spread disease and misery (much like early versions of vampires): however in later adaptations of the legend Revenants would develop more of a purpose and often returned from the grave in order to avenge themselves or others, either as an angry spirit or as a literal walking corpse.
Revenants have become a popular part of culture since their creation and some notable examples of Revenants in fiction would be the Crow and Spawn - they differ from zombies by the fact that they tend to retain human-level intelligence and often return to their slumber after exacting revenge, however some may be stuck in an eternal limbo.
The word Revenant derives from the French “revenir”, or “to return”. Revenant means one who has returned from the dead. They are considered as the origins of pop culture icons such as the vampire and Frankenstein’s Monster (who was the inspiration for the zombie). They could take on both spiritual and physical forms. In material form they could be anywhere from a freshly killed corpse to a plie bones that, oddly enough, would still bleed when cut. Some would attack men and drink their blood while others would eat everything but the blood. “The corpse of one revenant is reported to have been found in the grave, swollen and "suffused with blood". When it was pierced, a stream of blood flew out of the wound.” On top of that the bodies of these beasts would not burn unless the heart was removed. “[With] repeated blows of the blunted spade, and, thrusting in his hand, dragged out the accursed heart. This being torn piecemeal, and the body now consigned to the flames” They were often pointed at as the cause of spreading disease to the living. “[It was only after] the bodies of the revenants were exhumed, the heads cut off and their hearts removed, which put an end to the spread of the sickness.” Later, with the introduction to Christianity, they would also sprinkle the corpse with holy water for good measure in this process. Usually, they were said to rise from the dead to enact revenge on someone but, there were occasions that they would just terrorize the townspeople.
There were different classes of revenants (as the term revenant was thrown around so loosely). First there was the Nachzeher, a zombie-like creature focused on eating flesh instead of drinking blood. Vrykolakos, on the other hand, were bodies reanimated by the devil to torment others through the use of deception and terror. The Gespenst, were spirits whom roamed the earth searching for peace. This usually occurred after a violent death or if their body was left unburied. While the blutsauger and the vrikolax were what we would consider as Vampires known for blood hunger.