My auntâs kid is my cousin. My cousinâs kid and my kid are second cousins.
Itâs essentially finding the most recent common ancestor. My cousins and I share grandparents. Second cousins share great-grandparents, and so on.
âOnce removedâ and such refers to generational differences. So, my first cousinâs kid is my first cousin once removed, and my kidâs second cousin.
Someone with whom your most recent common ancestor is a great grandparent to both of you.
Like how a first cousin is someone with whom your most recent common ancestor is a grandparent to both of you (aka you both have a same grandparent but not a same parent - meaning one of each of your parents are siblings with each other).
If the most recent common ancestor isn't the same relation for both of you, then there's probably a "times removed" or one of you is some variety of aunt/uncle to the other.