A troika is a group of three people, or three countries, or three organisations, that work together and hold power together. You meet it mostly in news writing about politics and money: three leaders who run a party between them, or three institutions that together decide the terms of a loan to a country. It carries a faint sense that this group of three is powerful and acts as one body, and often a faint sense of distance or suspicion too — writers reach for it when the three are deciding something over other people's heads. The word is originally Russian, and its first meaning is concrete: a Russian carriage or sleigh pulled by three horses side by side. That older meaning still turns up in stories, in travel writing, and in the names of restaurants. So the picture behind the political sense is three horses harnessed together, pulling one vehicle — which is exactly the feeling the word gives: three separate powers, one direction. It is a journalist's and a historian's word, not an everyday one. In ordinary speech you would just say "the three of them".