The word ‘locus' and the phrase ‘locus standi' have been defined as follows in the Black's Law Dictionary, Revised 4th Edition, 1968:-
Locus. Lat. a place; a place where a thing is done.
Locus standi. A place of standing; standing in Court. A right to appear in a Court of justice, or before a legislative body, on a given question.
The plain meaning of the phrase is the entitlement of a person to appear before a Court of law. In earlier times, most of the litigation was between private parties. To deny a busybody or an inter loper, the right to approach a Court without any harm having been caused to him, this concept was developed. Only a person whose legal right had been violated or was likely to be violated was permitted to do so. This also curtailed unnecessary litigation.
Exceptions to the aforementioned rule have been created. A person who has substantial interest in the subject matter can also approach the Court. Even a person entitled to participate in decision making process which has resulted in a decision challenged before the Court has been held to possess locus standi. Persons having statutory rights also possess locus standi. The rule has further been diluted so as to permit judicial redress for persons unable to approach the Court on account of some disability or being under a social or economic dis-advantage. In cases of public interest also, where, public injury is caused on account of failure to carry out constitutional or statutory obligations strict application of the rule is not enforced, provided the person approaching the Court does not have any ulterior motive in doing so.