This is the 170th most frequent Russian word.
часов
The Russian word "часов" means "hours" (genitive plural form or partitive form of "час").
In this sentence, 'часов' is in the genitive plural form, used to indicate possession ('of the clock').
Мне нужно купить батарейки для часов.
I need to buy batteries for the clock.
In this sentence, 'часов' denotes a period of time (hours) in the genitive plural form to indicate an approximate duration.
Мы будем гулять около трех часов.
We will walk for about three hours.
In this sentence, 'часа' is used in the genitive singular form to express a specific time duration, whereas 'часов' would be used for numbers five and above.