Collateral relationships are relationships between individuals who descend from common ancestors but who are not related to each other in a direct line. Collateral relationships include your

• siblings,
• aunts and uncles,
• nieces and nephews , and
• cousins.
  

Full cousins are individuals who descend from common ancestors by the same number of generations.

• First cousins have in common two grandparents and their ancestors.
• Second cousins have in common two great-grandparents and their ancestors.
• Third cousins have in common two great-great-grandparents and their ancestors.

Individuals who descend from common ancestors by a different number of generations are cousins removed. The term once removed indicates a difference of one generation, twice removed a difference of two generations. For example,

• your first cousin’s child is your first cousin once removed
• your first cousin’s grandchild is your first cousin twice removed
• your father’s first cousin is your first cousin once removed
  
• your grandfather’s first cousin is your first cousin twice removed.