In most of North America, the 4-6-4 wheel arrangement is called a Hudson.
The notation describes four leading wheels, six coupled driving wheels, and four trailing wheels. The arrangement first appeared on a French locomotive and was known there as a Baltic, but North American railroads adopted the name Hudson after the New York Central introduced its version in 1927.
Hudsons were designed mainly for fast passenger service. Their four-wheel trailing truck supported a larger firebox and helped produce the sustained steam power needed for long express trains. They were especially effective on relatively level routes, where high speed mattered more than maximum starting tractive effort.
A common mix-up is confusing Hudson with Pacific. A Pacific is a 4-6-2, with only two trailing wheels, while a Berkshire is a 2-8-4 and a Mikado is a 2-8-2. Canada also used the Hudson name, including Canadian Pacific's famous semi-streamlined Royal Hudsons.