system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: What does "3rd cousin, twice removed" means? What's a 3rd cousin? How was he removed twice?
gpt
Your first cousin has the same grandparents as you, but not the same parents, right? Go back another generation, with your great-grandparents. Someone who also has the same great-grandparents, but not the same grandparents, is your second cousin. Go back another step to your great-great-grandparents, and you get your third cousins.

Your parents also have first cousins, these are your first cousins once removed (once removed = one generation up). They also have second cousins, they're your second cousins once removed. Your grandparents also have first, second, and third cousins - they're your first, second and third cousins twice removed (again, two generations up = twice removed).