Other forms: cousins
If Aunt Sally has a kid, that kid is your cousin, and if Aunt Sally's kid has a kid, and you have a kid too, then your kid and Sally's kid's kid are second cousins.
A cousin is a relative that's farther from you than an immediate relation like your brother or sister, usually the child of your aunt or uncle. Depending on how many children are born into your family, you might have tons of cousins you've never even met, like your distant cousin Johnny who went wild up in Alaska. We also use cousin to describe a kind of family resemblance between things, like the way barbecue sauce is the cousin of ketchup.