2-12-0 Definition
    noun
  
 Under the Whyte notation system, a steam locomotive that has a single-axle leading truck followed by six powered driving axles, and no trailing wheels.
 Wiktionary 
Under the Whyte notation system, a steam locomotive that has two leading wheels, six pairs of coupled driving wheels, and two trailing wheels.
 Wiktionary 
Under the Whyte notation system, a steam locomotive that has two leading wheels, six pairs of coupled driving wheels, and four trailing wheels.
 Wiktionary