Let’s ask wikipedia, shall we?!
“A system of degrees and removes is used to describe the relationship between …two cousins and the ancestor they have in common. The degree (first, second, third cousin, etc.) indicates the minimum number of generations separating either of the cousins from the common ancestor; the remove (once removed, twice removed, etc.) indicates the number of generations, if any, separating the two cousins from each other.
“…To work out if two people are first, second, or third cousins, count back the generations to their common ancestor. For example, if the common ancestor is one’s grandmother, that is two generations. If it is one’s great-grandmother, that is three generations.
“Identify the one of the two descendants who is generationally closest to the common ancestor. For example, if one of the cousins is a great-great-grandchild (four generations) and the other is a grandchild, the grandchild is generationally closest to the common ancestor.
“If the generationally closest descendant of the common ancestor is a grandchild (two generations), then the cousins are first cousins; if three generations separate the common ancestor and the generationally closest cousin, then the two are second cousins, and so on.
“If the cousins are separated from the common ancestor by an equal number of generations, there is no “remove,” for instance if both are grandchildren of the common ancestor.
“But if the number of generations between the common ancestor is different for each cousin, that difference is expressed by using a clarifier, “removed,” with the number of removes. For example, if one person is a grandchild of (2 generations from) the common ancestor, and the other person is a great-great-grandchild of (4 generations from) that common ancestor, then the two are first-cousins-twice-removed.”