The Leopard in Heraldry
A heraldic leopard is nearly identical to a heraldic lion. In fact, it looks like a lion only it is always passant guardant. The leopard is found most famously in the arms of England.
The Leopard in SCA Heraldry
When registering an SCA device, a heraldic leopard is considered the same as a lion for the purposes of conflict checking.
The Leopard in Medieval Bestiaries
The leopard is considered the bastard offspring of a lion and a pard. The leopard's reputation in literature is somewhat derogatory considering its noble role in heraldry.