This is the 1329th most frequent Russian word.
троих
The word "троих" in English means "three (of them)" or refers to "three people" in the genitive or accusative case.
The word 'троих' is used here as the genitive plural form in direct object form indicating the number of people.
Я купил билеты на троих.
I bought tickets for three people.
Here, 'троих' is used in the prepositional case, describing the specific people with whom the event occurred.
Мы виделись с троих вчера.
We met with three people yesterday.
The word 'троих' functions here in the accusative case, denoting the individuals who received the action of thanking.