What is a second cousin thrice removed?

The terminology like "second cousin thrice removed" can seem quite confusing. The table below (hopefully) clarifies these genealogical terms. Please note that this terminology is protestant English (please correct me if I'm wrong) and such nomenclature does not necessarily apply elsewhere.

Comman Ancestor	Child	Grandchild	Great Grandchild	Great Great Grandchild	3xGreat Grandchild	…
Child	Sibling	Nephew / Niece	(Great) Nephew / Niece	(Great Great) Nephew / Niece	(3 x Great) Nephew / Niece	. . .
Grandchild	Uncle / Aunt	(1st) Cousin	1st Cousin once removed	1st Cousin twice removed	1st Cousin thrice removed	. . .
Great Grandchild	Great Uncle / Aunt	1st Cousin once removed	2nd Cousin	2nd Cousin once removed	2nd Cousin twice removed	. . .
Great Great Grandchild	Great Great Uncle / Aunt	1st Cousin twice removed	2nd Cousin once removed	3rd Cousin	3rd Cousin once removed	. . .
3 x Great Grandchild	3 x Great Uncle / Aunt	1st Cousin thrice removed	2nd Cousin twice removed	3rd Cousin once removed	4th Cousin	. . .
. . .	. . .	. . .	. . .	. . .	. . .	.     .         .

How to use this table: Choose two people, whose relation you wish to consider, and determine their relationship to their common ancestor (child, grandchild, etc.). For the first person (call them A) locate their relationship to the common ancestor on the first row. For the second person (B) locate their relationship to the common ancestor on the first column. The cell where the corresponding column and row intersect describes the relationship of person A with respect to person B.

For example (see below), suppose Mary and John have a common ancestor, Frank. Mary is Frank's grandchild and John is Frank's great great great grandchild. Placing Mary on the first row in the "Grandchild" spot and John on the first column in the "3 x Great Grandchild" spot, the intersection of the column and row shows that Mary is the 1st cousin three times removed from John.

Comman Ancestor (Frank)	Child	Grandchild (Mary)
Child	Sibling	Nephew / Niece
Grandchild	Uncle / Aunt	(1st) Cousin
Great Grandchild	Great Uncle / Aunt	1st Cousin once removed
Great Great Grandchild	Great Great Uncle / Aunt	1st Cousin twice removed
3 x Great Grandchild (John)	3 x Great Uncle / Aunt	1st Cousin thrice removed

Ladder view

Another (perhaps more convenient) way to look at this is like a ladder with the common ancestor at the top. The relationship between any two people at the same “rung” will be siblings or first cousins or second cousins or third cousins, etc.

Common Ancestor     |   |   | |   | Person A siblings Person B |   | |   | |   | Person C 1st Cousins Person D |   | |   | |   | Person E 2nd Cousins Person F |   | |   | |   | Person G 3rd Cousins Person H |   | |   | |   | Person I 4th Cousins Person J |   | etc.   etc.

The “removal” number is calculated by the number of steps you need to make to put two people on the same rung, closest to the common ancestor. For example, what is the relationship between Person C and Person H (see above)? Since Person C is closest to the common ancestor, the relationship will start with “1st cousin”, but because Person H is 2 rungs below Person C, the actual relationship is 1st cousin, twice removed. Note that in this picture the relationship between the first rung (siblings) and the second rung (1st cousins) is the uncle/aunt-niece/nephew relationship (so you could say, although you never would, that an uncle and niece are actually zeroth cousins, once removed).