What is a cousin?
A cousin is a relative with whom a person shares one or more common ancestors. The most common ancestor is a grandparent. In the general sense, cousins are two or more generations away from this common ancestor, thus distinguishing a cousin from an ancestor, descendant, sibling, aunt, uncle, niece, or nephew. Systems of “degrees” and “removals” are used in the English-speaking world to describe the exact relationship between two cousins and the ancestor they have in common. Various governmental entities have established systems for legal use that can more precisely specify kinships. With common ancestors existing any number of generations in the past, though common usage often eliminates the degrees and removals and refers to people with common ancestry as simply “distant cousins” or “relatives”. The ordinals in the terms “first cousins”, “second cousins”, “third cousins”, refer to the number of generations to one’s closest common ancestor. The number of “Great” used to describe this ancestor will determine how close the relationship is, for example, having a “Great-Great-Grandparents” in common would be third cousins.
When the cousins are not the same generation, they are described as “removed”. In this case, the smaller number of generations to the common ancestor is used to determine the degree, and the difference in generations determines the number of times removed. Note that the ages of the cousins are irrelevant to the definition of the cousin relationship. 
1. “Genetic And Quantitative Aspects Of Genealogy – Types Of Collateral Relationships”. Genetic-genealogy.co.uk. Retrieved 28 October 2014.