This is the 1568th most frequent Russian word.
рождения
"Рождения" means "birth" in English.
The word 'рождения' is used here to denote the genitive case in the phrase 'день рождения', which translates to 'birthday'.
День рождения моего друга был на прошлой неделе.
My friend's birthday was last week.
The word 'рождения' is used in its genitive form to mean 'of birth' within the prepositional phrase describing possession.
Она не знает точной даты своего рождения.
She does not know the exact date of her birth.
The word 'рождения' appears to indicate the genitive case in the construction 'со дня рождения', which specifies 'from the day of birth' in the context of an anniversary.