A sibling who you do not have the same parents as. HALF siblings either have the same mother only, or the same father only.
Since Wendy and Sally are sisters, and they do not have same father, they are Half Siblings.
by Fame Hungry June 17, 2009
A brother or sister that have the same mama and a different daddy...
"We don't know who mama's baby daddy is, but the little bastard's gonna be my half sibling..."
by -KTG February 14, 2008