Frederick Methvan Whyte's system of classification is used to describe the wheel arrangement of conventional steam locomotives. The first number is the number of leading wheels, The middle number (or numbers) give the number and arrangement of driving wheels, and the last is the number of trailing wheels. "T" at the end denotes a tank engine.
Whyte was a Dutch New York Central mechanical engineer. Often seen spelled "F. M. White".
WHYTE CLASSIFICATION OF LOCOMOTIVES BY WHEEL ARRANGEMENT

Symbol

Wheel Arrangement (Front to Back)

Type Name

0-6-0 OOO Six-wheel switcher
0-8-0 OOOO Eight-wheel switcher
2-6-0 oOOO Mogul
2-6-2 oOOOo Prairie
2-8-0 oOOOO Consolidation
2-8-2 oOOOOo Mikado
2-8-4 oOOOOoo Berkshire
2-10-0 oOOOOO Decapod
2-10-2 oOOOOOo Santa Fee
2-10-4 oOOOOOoo Texas
4-4-0 ooOO American
4-4-2 ooOOo Atlantic
4-6-0 ooOOO Ten-Wheeler
4-6-2 ooOOOo Pacific
4-6-4 ooOOOoo Hudson (Baltic)
4-8-2 ooOOOOo Mountain
4-8-4 ooOOOOoo Northern
4-8-8-4 ooOOOO OOOOoo "Big Boy"