This is the 966th most frequent Czech word.
předchozí
"Previous" or "preceding."
In this sentence, 'předchozí' is used as an adjective to describe the day that came before.
Předchozí den byl deštivý.
The previous day was rainy.
Here, 'předchozí' acts as an adjective, attributive, to specify which lesson was studied.
Studoval jsem předchozí lekci.
I studied the previous lesson.
'Předchozí' is functioning as an adjective here as well, clarifying which decision is being referred to.