This is the 5808th most frequent Russian word.
пятьдесят
Fifty.
The word "пятьдесят" is used as a numeral to quantify the number of apples.
Мне нужно купить пятьдесят яблок.
I need to buy fifty apples.
Here, "пятьдесят" quantifies the amount of money, rubles.
В конверте лежало пятьдесят рублей.
There were fifty rubles in the envelope.
In this sentence, "пятьдесят" indicates the number of students who attended the conference.