Natural latex is made of rubber tree sap.  The back of the rug is covered with the rubber and either baked on or left to air dry.  This backing is mostly applied for the stability of the weave to keep it straight, but it can act as a non-skid surface.  Keep in mind that with the large number of different flooring finishes and cleaners it is possible the backing can react with the floor, causing it to flake or stick.  Depending on your flooring type of finish a rug pad between the rug and floor might be recommended.