What is the difference between somebody having really pale skin and being an albino?

Genetics mostly. Albinism is a genetic defect in which melanin production is completely inhibited. Besides having white skin, people with albinism have several other manifestations (i.e. Certain hair and eye colors). Someone with pale skin just does not produce much melanin. These individuals tend to have roots from northern latitudes. They can actually tan, while people with albinism cannot tan.