Plaza was the name of a hotel on Fifth Avenue, in New York City. This hotel was where the wealthy traveler, on a visit to the city, would book a room in the early 20th century. A typical room, or apartment, might have a bedroom and a reception room. This hotel was equipped with the latest in technology, including telephones.
In The Big Good-Bye, the master criminal Silent Forrester booked a room on the twelfth floor. This room's telephone was bugged by the police who took up residence in a room on the eleventh floor. Detective Jim Tierney and his squad recorded what was transmitted on the telephone wires. Later, three females would call Forrester at his suite, and he would elude the police. (TNG: "The Big Goodbye")