Heir apparent

An heir apparent, sometimes femininely heiress apparent, frequently regularly heir, is a person who is first in an order of succession and cannot be displaced from inheriting by the birth of another person; a person who is first in the order of succession but can be displaced by the birth of a more eligible heir is known as heir presumptive.

Today these terms most commonly describe heirs to hereditary titles (e.g. titles of nobility) or offices, especially when only inheritable by a single person. Most monarchies refer to the heir apparent of their thrones with the descriptive term of crown prince or crown princess, but they may also be accorded with a more specific substantive title such as Prince/Duke of (region).

The term is also used metaphorically to indicate an expected successor to any position of power, e.g. a political or corporate leader.

Heir Apparent versus Heir Presumptive
In a hereditary system governed by some form of primogeniture, an heir apparent is easily identifiable as the person whose position as first in the line of succession to a title or office is secure, regardless of future births. An heir presumptive, by contrast, can always be "bumped down" in the succession by the birth of somebody more closely related in a legal sense (according to that form of primogeniture) to the current title-holder.

The clearest example occurs in the case of a childless bearer of a hereditary title that can only be inherited by one person. If at any time the title bearer were to produce children, those children would rank ahead of any person who had formerly been heir presumptive.