The term "nub" can have multiple meanings depending on its context.
In a general sense, it could refer to a small rounded mass or projection, often used in reference to something that protrudes outwards from an object such as a tree branch ending abruptly or the end of a gun barrel.
The term "nub" can also be used metaphorically to describe a shortened version of something, for example: "I gave him the nub of it." This means that I only told him the most important part and left out unnecessary details.
In additionally, in some regions of Africa, particularly Sudan, "nub" is used as an ethnic group name referring to people who inhabit areas along the Nile River in northern Sudan.