Carrier
Carrier means the operator of any airline, railroad, motor carrier, shipping line, or other enterprise which is engaged in the business of transporting any animals for hire. Except anyone transporting a migratory bird covered under the Migratory Bird Treaty Act from the wild to a facility for rehabilitation and eventual release in the wild, or between rehabilitation facilities, and has obtained authorization from the U.S. Fish and Wildlife Service for that purpose, is not a carrier.
Source
9 CFR § 1.1
Scoping language
For the purposes of this subchapter, unless the context otherwise requires, the following terms shall have the meanings assigned to them in this section. The singular form shall also signify the plural and the masculine form shall also signify the feminine. Words undefined in the following paragraphs shall have the meaning attributed to them in general usage as reflected by definitions in a standard dictionary.