Organic usually mean living things.. plants, animals, people , etc
Non-organic, cars, machines, houses, furniture
This is not to say that one or the other cannot have features from both categories such as a toy stuffed lion is still and organic shape eventhough it is not living. A coffee maker could have an organic HR Giger look to it but still have "hard surfaces".
Generally speaking orgranic surfaces have more curves and continous surfaces whereas hard surface have parts and sharp angles and more rigid straight lines in them.
Another difference is that it is implied that most organic usrfaces are deformable and therefore may require special treatmetn to do so whereas hard surface do not and might have less desnse meshes are less evenly spaced meshes. A hard surface would not need extra iosparms in the elbows so that they deform correctly when bent.