According to Wikipedia,
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 "G" words used to describe this ancestor will determine how close the relationship is. For example, having "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.
The article goes on to list and explain a host of other types of cousins. There are double-cousins, half-cousins, step-cousins, cousins-in-law, and maternal versus paternal cousins. Needless to say, it can get rather complicated.
Things are greatly simplified in Heaven. There everyone will be your brother or your sister in Christ. Our earthly relations will pale in significance when compared to our common spiritual ancestry in Christ.
"He replied to him, 'Who is my mother, and who are my brothers?' Pointing to his disciples, he said, 'Here are my mother and my brothers' " (Matthew 12:48-49).