understanding family relationships

[archersangel]

if you have trouble understanding the whole first cousin once removed & second cousin thing, this chart explains who is who.

but it doesn't go into my personal pet peeve of people not knowing the difference between step-siblings & half-siblings.
according to wikipedia,

"Stepsiblings" (stepbrothers or stepsisters) are the children of one's stepparent from a previous relationship. They are unrelated by blood.
Half-siblings share only one parent instead of two as full siblings do and are on average 25% related,[3] in other words, the children that the parent and stepparent (the mother and stepfather, or the father and stepmother) or previous partner have together.