In base is an heraldic term, referring to a charge based toward the bottom of the shield. It contrasts with in chief -- charges placed in the uppermost quarter to one-third of the field of a shield -- but in base does not have the same firm implication of proportions.
It would be unusual for a charge to be in base if there is no charge in chief -- where there is a chief, a separate charge, this would be disregarded in terms of describing the main area.
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