This is the 13000th most frequent Russian word.
лошадь
Horse.
Here, 'лошадь' is used as the subject noun of the sentence to refer to an animal.
На ферме пасется лошадь.
There is a horse grazing on the farm.
The word 'лошадь' is used as a direct object, referring to a horse acquired for riding.
Она купила новую лошадь для верховой езды.
She bought a new horse for horseback riding.
'Лошадей' is the plural form of 'лошадь' in the accusative case, referring to horses in general.