The term "Subway Tile" has been in use since the early 1900's. The New York subway system opened in 1904 and the term became more prevalent.
The usage of "Subway Tile" as a phrase has changed significantly over the years. Originally it was used to refer to the beautiful mosaics in the New York subway system but now is generally in reference to the 3" x 6" size that has commonly been associated with the subway.
The material used in New York consists mostly of white ceramic tile with the mosaics being made of various colors in order to form elaborate designs. Now "Subway Tile" is often made of ceramic or glass. Ceramic is more indicative of the actual tile used in the subway system as well as often used in period homes around the area. Ceramic subway tile to match the given period is readily available online.
A newer trend in subway tile is the addition of glass. Glass offers the classic, time tested look of New York subway tile but with the contemporary twist of a more modern material. Glass is less absorbent, more durable and generally more aesthetically pleasing than ceramic.
Whatever material, color, or size you choose of Subway Tile you will certainly enjoy the look and feel it offers!