1) Indefeasible legatee 2) Next in line to a throne 3) Person set to to succeed 4) Virtual reality in fiction 
An heir apparent is a person, male or female, who is first in line of succession and cannot be displaced from inheriting by the birth of another person. An heir presumptive, by contrast, is someone who is first in line to inherit a title but who can be displaced by the birth of a more eligible heir. Today these terms most commonly describe heirs t...
(from the article `heir`) One may be either heir apparent or heir presumptive during the lifetime of the property holder. The heir apparent is one whose right to inherit is ...
(n) Heir Apparent is the person expected to inherit a property of a person on his death by being his or her legal heir, when he survives after the death of the owner
One who is expected to inherit property from the estate of a family member.
An heir-apparent is someone who 'are such whose right of inheritance is indeafsible provided they outlive the ancestor; as the eldest son, who must be heir to the father when ever he happens to die'. Blackstone. That is, someone whose right of inheritance cannot be superseded by the birth of another, unlike an heir-presumptive whose right of inheri...
[n] - an heir whose right to an inheritance cannot be defeated if that person outlives the ancestor
heir apparent After death the heir apparent becomes the heir-at-law.