Grand Central Terminal (GCT) is a commuter (and former intercity) railroad terminal at 42nd Street and Park Avenue in Midtown Manhattan in New York City. Built by and named for the New York Central Railroad in the heyday of American long-distance passenger rail travel, it is the largest such facility in the world by number of with 44 serving 67 tracks along them. They are on two levels, both below ground, with 41 tracks on the upper level and 26 on the lower, though the total number of tracks along platforms and in rail yards exceeds 100. The terminal covers an area of 48 acres.

The terminal serves commuters traveling on the Metro-North Railroad to Westchester, Putnam, and Dutchess counties in New York State, and Fairfield and New Haven counties in Connecticut. Until 1991 the terminal served Amtrak, which moved to nearby Pennsylvania Station upon completion of the Empire Connection.
Although the terminal has been properly called “Grand Central Terminal” since 1913, it has "always been more colloquially and affectionately known as Grand Central Station", the name of the previous rail station on the same site, and of the U.S. Post Office station next door, which is not part of the terminal. It is also sometimes used to refer to the Grand Central – 42nd Street subway station, which serves the terminal.

The Main Concourse is the center of Grand Central. The space is cavernous – 275 ft (84 m) long, 120 ft (37 m) wide and 125 ft (38 m) high and usually filled with bustling crowds. The ticket booths are in the Concourse, although many now stand unused or have been repurposed since the introduction of ticket vending machines. The large American flag was hung in Grand Central Terminal a few days after the September 11 attacks on the World Trade Center. The main information booth is in the center of the concourse. This is a perennial meeting place, and the four-faced clock on top of the information booth is perhaps the most recognizable icon of Grand Central. The clock, designed by Henry Edward Bedford and cast in Waterbury Connecticut, is made from brass. Each of the four clock faces is made from opalescent glass (now often called opal glass or milk glass), though urban legend has it that the faces are made of opal and that Sotheby's and Christie's have estimated their value to be between $10 million and $20 million. A 1954 New York Times article on the restoration of the clock notes that "Each of the glass faces was twenty-four inches in diameter...". Within the marble and brass pagoda lies a "secret" door that conceals a spiral staircase leading to the lower-level information booth.