What is Apparent Heir?

Legal Definition
In English law. One whose right of inheritance is indefeasible, provided he outlive the ancestor. 2 Bl. Comm. 208. In Scotch law. He is the person to whom the succession has actually opened. He is so called until his regular entry on the lands by service or infeftment on a precept of dare constat.
-- Black's Law Dictionary
Legal Definition
One who will inherit if he survive the ancestor.
-- Ballentine's Law Dictionary