Past anterior (Preterite perfect)
El Pretérito Anterior also known as El Antepretérito
Currently, El Pretérito Anterior is pretty much only used in written texts to express a past fact that happened immediately before another that is linked to it, that also happened in the past.
El Pretérito Anterior is formed with:
En cuanto hubo terminado su trabajo, se fue a comer.
As soon as he had finished his work, he went to eat.
Tan pronto como Carla hubo cobrado, se compró un coche.
As soon as Carla had received her salary, she bought a car.