Is a first cousin a blood relative?

All cousins are so-called "blood relatives." This applies to first cousins, to fifth cousins, to second cousins twice removed and to sixth cousins ten times removed. Being cousins of any sort means you and they are descended for some common ancestor somewhere.

For example: your mother's first cousin is your first cousin, once removed. This is because your mother's first cousin is one generation younger than your grandparents and you are two generations younger than your grandparents. This one-generation difference equals "once removed."