Depending on their gender, children who have the same mother but separate fathers are referred to as half-siblings, half-brothers, or half-sisters. Two children that have separate moms but the same father can also be considered half-siblings.
Children who share the same mother and father are considered traditional siblings. Children who are step-siblings do not share a biological parent and whose parents married after the children were born.
Adoptive siblings are two children who are not biologically related but who were adopted by the same parents, whereas foster siblings are children reared together in the same foster home. Cross siblings are two kids who do not share a parent but do have one or more half-siblings in common.