What is the definition of "a person aids and abets the commission of a crime"?

"A person aids and abets the commission of a crime when he or she, (i) with knowledge of the unlawful purpose of the perpetrator, (ii) and with the intent or purpose of committing, facilitating or encouraging commission of the crime, (iii) by act or advice, aids, promotes, encourages or instigates the commission of the crime." (People v. Cooper (1991) 53 Cal.3d 1158, 1164.)