Nubuck and leather are not different because they are both leather. Nubuck is a type of leather that has had the grain brushed and polished, but not processed. Most leather has had some type of processing on it.
Full-grain leather is a type of leather that has not been processed at all and has the original markings of the animal that it came from. The characteristics of the leather vary greatly depending on the type of animal. It is among the most natural leathers.
Leathers, such as nubuck, have only been treated to an extent that they are brushed and polished. These fall into the aniline leather groups, although they are not true aniline leather. Aniline is among the most expensive and makes up the smallest percentage of leather in the world. Aniline leather can be distinguished by the lighter color it receives when it is lightly scratched.
Top-grain leather is among the most processed and most popular option as a type of leather. It has had the top layer buffed, polished and treated. This group of leathers includes the most common corrected leather. These leathers are treated to make them more uniform and will eliminate any imperfections that could have been found on the animal's hide.