This is the 9286th most frequent Polish word.
trzej
"Trzej" means "three" (masculine, nominative plural form) in English.
The word 'trzej' is used here as a numeral to denote three masculine individuals in nominative case.
Trzej przyjaciele poszli na wycieczkę.
Three friends went on a trip.
The word 'trzej' changes to 'trzech,' showing its genitive form to agree with the context.
Spotkałam trzech mężczyzn w parku.
I met three men in the park.
Here 'trzech' is used in locative case to indicate the context of 'about three boys.'