Skin contact is the process in which the grape skins are soaked in the juice remaining after the grapes have been destemmed and crushed for a certain period of time.
This skin contact is essential when brewing red wine.
On the other hand, it is common for white wine to not go through this process, but some producers may use skin contact with white wine in order to transfer the components in the skins to the juice.
Therefore, when the term "skin contact" is used, it usually refers to the infusion of fruit skins during the brewing process of white wine.
In French it is called macération pelliculaire.