What is the definition of "aider and abettor"?

"'[A]n aider and abettor is a person who, "acting with (1) knowledge of the unlawful purpose of the perpetrator;... (2) the intent or purpose of committing, encouraging, or facilitating the commission of the offense[; and] (3) by act or advice aids, promotes, encourages or instigates, the commission of the crime."' [Citations.]" (People v. Jurado (2006) 38 Cal.4th 72, 136.) Such person "'need not have intended to encourage or facilitate the particular offense ultimately committed by the perpetrator'" and need not have "'the specific intent that is an element of the target offense....' [Citation.]" (People v. Prettyman (1996) 14 Cal.4th 248, 261.) An aider and abetter is liable for any crime committed by the person he or she aids and abets "that is the 'natural and probable consequence' of the target crime." (Ibid.) "[A]dvance knowledge is not a prerequisite for liability as an aider and abettor. 'Aiding and abetting may be committed "on the spur of the moment," that is, as instantaneously as the criminal act itself. [Citation.]' [Citation.]" (People v. Swanson-Birabent (2003) 114 Cal.App.4th 733, 742.)