Basically, for Batak people, if you want to marry it's vest to marry your Pariban. Also, several surnames (marga) can be considered the same marga family, as they were descended from a common ancestor. You may note that cousins might be called Pariban. Yes, the term actually means a specific type of cousin, and the "best" Pariban to marry is your own cousin. No one does that anymore, though. Small interesting thing : only men can recognize who their Pariban is at first, since you don't usually know surnames of other people mothers.