What would you call your grandpa's brother's daughter?

She's basically your mom or you dad's cousin. And Your parent's first cousin is your first cousin once removed.

The child of your first cousin is also your first cousin once removed: your grandparent is that child's great-grandparent. You can do the whole "removed" thing for every category of cousins -- second cousin once removed, and so on.

Having trouble coming up with the proper term for your mother's uncle's father for your family tree? Here's a guide to who's who in the family structure from BHG.com.

To further determine the relationship between any two people in a family tree, see GenealogyInTime.com's The Key to Understanding Family Relationships.