This is the 290th most frequent Russian word.
субботу
"Субботу" means "Saturday" (accusative case) in English.
The word 'субботу' here represents the accusative case of the day 'Saturday', indicating the time when the action (going to the park) will occur.
Я пойду в парк в субботу.
I will go to the park on Saturday.
The word 'по субботам' is in the dative plural form and implies a repeated activity that happens on Saturdays.
Мы часто смотрим фильмы по субботам.
We often watch movies on Saturdays.
The phrase 'в прошлую субботу' uses 'субботу' in the accusative case, modified by 'прошлую' to indicate a specific past Saturday as the time of occurrence.