Great-grandparents
The parents of a grandparent, or the grandparents of a parent are called all the same names (grandfather/-mother, grandpa/-ma, granddad/-ma, etc.) with the prefix great- added, one for each additional generation. One's great-grandparent's parents would be "great-great-grandparents". To avoid a proliferation of "greats" when discussing genealogical trees, one may also use ordinals instead of multiple "greats"; thus a "great-great-grandfather" would be the "second great-grandfather", and a "great-great-great-grandfather" would be a third great-grandfather, and so on. This system is used by some genealogical websites such as Geni. Individuals who share the same great-grandparents but are not siblings or first cousins are called "second Cousins" to each other, as second cousins are the grandchildren of one's grandparent's siblings.
Read more about this topic: Grandpa