Where does the expression “to flog a dead horse” come from and What does it mean?

The expression “to flog a dead horse” means: To try to revive a feeling of interest that has died; to engage in a fruitless undertaking.

The French express it more literallychercher a ressusciter un mort, to seek to resuscitate a corpse.

But whatever the language, the sense is clear: it is as useless to try to stir up interest in an issue that is dead as it would be to try to get a dead horse to pull a load by flogging it.