11 CFR 9032.2: Candidate.

Candidate means an individual who seeks nomination for election to the office of President of the United States. An individual is considered to seek nomination for election if he or she—

(a) Takes the action necessary under the law of a State to qualify for a caucus, convention, primary election or run-off election;

(b) Receives contributions or incurs qualified campaign expenses;

(c) Gives consent to any other person to receive contributions or to incur qualified campaign expenses on his or her behalf; or

(d) Receives written notification from the Commission that any other person is receiving contributions or making expenditures on the individual's behalf and fails to disavow that activity in writing to the Commission within 30 calendar days after receipt of notification.