A giant is a tall Heavy Unit, and a powerful combatant.
Real World References
The Western Giants refer to the San Fransisco Giants of baseball.
If there are Eastern Giants, that could refer to the New York Giants of football.
Other sports giants include the Tokyo Yomiuri Giants (baseball), the Manchester Giants (basketball), the Delhi Giants (cricket) and the New York Giants (soccer), or the Vancouver Giants (hockey). Then there are other possibilities, like Forest-based Green Giants, etc.