Geared steam locomotive
A geared steam locomotive is a type of steam locomotive which uses gearing, usually reduction gearing, in the drivetrain, as opposed to the common directly driven design.
Fairlie locomotive
In both the UK and the USA, single Fairlies were the first locomotives in each country to use the European Walschaerts valve gear. The Stephenson link gear, which was usual at the time, used multiple eccentrics between the frames but the Walschaerts gear was mounted "outboard" of the frames and connecting rods. This was advantageous because the Fairlie system required this space between the frames for the bogie pivot.