COUSINS
First ... second ... third cousins
once ... twice removed
?@#!
Cousins share a common ancestor at least two generations back.
First cousins have one pair of grandparents in common. For example:
Peter Jones is [first] cousin to Adam and Susan Smith because they share
grandparents John and Ann Smith
Walter Smith is second cousin to Lucy and Rebecca Jones because they
share great-grandparents but not grandparents.
Joseph Smith is third cousin to Rachel Williams because they share
great-great-grandparents ...
Fourth cousins would share a pair of great-great-great-grandparents
And so on.
When a cousin is described as 'once removed' it means that one of the
cousins is a generation further away from the common ancestor
than the other. For example:
Peter Jones is first cousin to Adam Smith.
Peter's children Lucy and Rebecca also have Adam Smith as a first
cousin, but in their case the relationship is 'once removed' because
they are one more generation away from the common ancestors than
Adam.
Lucy's daughter Rachel is also first cousin to Adam Smith, but now
the relationship is 'twice removed'.
So the children, grandchildren, great-grandchildren, etc, of your
first cousin are also your first cousins, once removed, twice
removed, and three times removed respectively.