The Spanish pluperfect subjunctive resembles the English past perfect subjunctive because it is used to describe unreal actions or situations in the past, i.e., actions or situations that could have happened but never came to fruition. It is formed by using hubiera/hubiese, the imperfect subjunctive of the verb haber, + the past participle of the verb that describes the action or state.

Ojalá hubiese comprado boletos para el concierto.

It is also used to express the negative belief of a certainty in the pluperfect of the indicative mood.

Positive pluperfect indicative: Teresa había estudiado toda la noche.

Negative pluperfect subjunctive:  No creo que Teresa hubiera/hubiese estudiado toda la noche.