The right of a party to initiate an action and be heard before a Court of law is called

The correct choice is: “Locus standi”

Locus standi (Latin, “place of standing”) is the right or capacity of a person to bring an action and be heard before a court. Traditionally only a person whose own legal right was affected had locus standi; Indian courts relaxed this rule for public interest litigation (for example, in S.P. Gupta v. Union of India, 1981).

A “Right in rem” is a right available against the whole world (such as ownership), and a “Right in personam” is a right available against a particular person (such as a contractual right). A “Fundamental right” is a right guaranteed by Part III of the Constitution. None of these describes the capacity to sue.