A set of beleifs designed to explain the unanswerable questions of this world because people, apparently, can't handle things they don't understand. Although lots of these things have now been explained through science, people still refuse to let go of religion, because they now can't handle to see the truth and this falsehood provides a comfort that a life in this worhtless world will utlimately lead to a greater happiness (or afterlife).
Religion has also been used as the justification for murder and various other acts seen as wrong, even though these acts are against the teachings of the religion.
Of course their is no proof of whether any religion can be considered false or true, and this can probably only be discovered in death.
If there was one true religion, surely we'd know about it