Final answer:
A paraphyletic group of organisms includes a common ancestor and some but not all of its descendants.
Step-by-step explanation:
A paraphyletic group of organisms is a group that includes a common ancestor and some but not all of its descendants. It does not include all the descendants of a common ancestor, but rather excludes one or more descendant groups. For example, if we have a group that includes mammals and reptiles but excludes birds, it would be considered a paraphyletic group. Paraphyletic groups are not considered clades, which are groups that include all descendants of a common ancestor.