Caucuses

A caucus is a meeting of supporters or members of a specific political party or movement. The term originated in the United States, but has spread to Australia, Canada, New Zealand, South Africa and Nepal. As the use of the term has been expanded, the exact definition has come to vary among political cultures.

The origin of the word caucus is debated, but it is generally agreed that it first came into use in the British colonies of North America.

A February 1763 entry in the diary of John Adams of Braintree, Massachusetts, is one of the earliest appearances of Caucas, already with its modern connotations of a "smoke-filled room" where candidates for public election are pre-selected in private:

This day learned that the Caucas Clubb meets at certain Times in the Garret of Tom Daws, the Adjutant of the Boston Regiment. He has a large House, and he has a moveable Partition in his Garrett, which he takes down and the whole Clubb meets in one Room.
There they smoke tobacco till you cannot see from one End of the Garrett to the other. There they drink Phlip I suppose, and there they choose a Moderator, who puts Questions to the Vote regularly, and Selectman, Assessors, Collectors, Wardens, Fire Wards, and Representatives are Regularly chosen before they are chosen in the Town...

An article in Great Leaders and National Issues of 1896, surveying famous presidential campaigns of the past, begins with an unsourced popular etymology of the origin of the caucus:

The Origin of the "Caucus"
The presidential nominating convention is a modern institution. In the early days of the Republic a very different method was pursued in order to place the candidates for the highest office in the land before the people.
In the first place, as to the origin of the "caucus." In the early part of the eighteenth century a number of caulkers connected with the shipping business in the North End of Boston held a meeting for consultation. That meeting was the germ of the political caucuses which have formed so prominent a feature of our government ever since its organization.

...
Wikipedia