Embryo. The initial stage of an animal's development after collection from the natural mother, while it is capable of being transferred to a recipient dam, but not including an embryo that has been transferred to a recipient dam.
9 CFR § 98.2
The following terms, when used in this subpart, shall be construed as defined. Those terms used in the singular form in this subpart shall be construed as the plural form and vice versa, as the case may demand.