The keyboard shortcut for Select Parents is Alt+Up (Windows) or (Mac). (Think “Up the family tree.”)
The parents of an object are those objects upon which the object directly depends. For example, a segment’s parents are the endpoints used to define it and a midpoint’s parent is the segment on which it’s constructed.
If the selected object has no parents (in other words, if it’s an independent object), it remains selected. If the parents of the selected object are hidden, then the selected object is deselected (leaving nothing selected).