Subway tiling is one of the many kinds of tiling which is extremely popular this day. A lot of people using them to tile kitchen splash backs, feature walls in the bathrooms or powder rooms etc.
They can be laid as in normal stuck bond pattern but also in brick pattern which is most popular out of all patterns. Many interior designers like them to be laid in herringbone pattern.
Classic subway tiles are ceramic or marble but this days there are no limit for the materials (glass, terracotta, porcelain, granite etc.)
That trend came to us from early twentieth from New York city subway stations, where they used them to tile walls. Most designers would agree that subway tiles are not going out of style anytime soon.