A nectarine is like a peach - except it has smooth skin instead of fuzzy skin of a peach. It is like a combination of a peach and a plum. Mandarins are a class of oranges --a citrus fruit that you can easily peel. Clementines are a type of mandarin. Clementines are the smallest member of the mandarin family and are seedless. The peel is smooth, glossy and deep orange.

Here is another reference to the different types of oranges in the orange family.