A more thorough explanation:

Term: quoad excessum
Definition: Quoad excessum is a Latin term that means "with regard to the excess." It is used in legal contexts to refer to situations where a provision or donation made by one person to another is excessive and therefore subject to revocation. For example, if a husband makes a postnuptial provision for his wife that is commensurate with his circumstances and natural duty, it cannot be revoked by him as a donation. However, if the provision is immoderate or excessive, it may be revoked quoad excessum, insofar as it exceeds what is reasonable or necessary. This means that the excess portion of the provision can be revoked, but the rest of it remains valid. For instance, if a husband gives his wife a large sum of money that is far beyond what she needs or what he can afford, he may be able to revoke the excess amount, but not the entire gift.