This is the 370th most frequent Czech word.
oba
"Oba" means "both" in English.
"Oba" is used as a quantifier referring to two entities (the brothers) as a collective unit.
Oba bratři šli do parku.
Both brothers went to the park.
"Oba" is used to specify that the speaker has seen both items in a pair (movies).
Viděla jsem oba filmy, které jsi doporučoval.
I watched both movies you recommended.
"Oba" refers to two subjects who share a common preference or action (enjoying the summer by the water).