@Letty,
It refers to "cousins" who are ELIGIBLE to marry.
Don't get grossed out; it can happen innocently enough:
Consider Mr. A married to Mrs. B.
All of Mr. A's siblings' children refer to him as "Uncle" and to his wife as "Aunt".
Similarly, Mrs. B's siblings' children refer to her as "Aunt" and to her husband as "Uncle".
At family reunions, they are regarded as "cousins" (having an Aunt and Uncle in common), but they do not have any actual consanguinity, and are as marriageable to each other as were Mr. A and Mrs. B in the first place.
In other words, they may "kiss".