Here it is:
[A] mythical creature of the law whose conduct is the standard by which the Courts measure the conduct of all other persons and find it to be proper or improper in particular circumstances as they may exist from time to time. He is not an extraordinary or unusual creature; he is not superhuman; he is not required to display the highest skill of which anyone is capable; he is not a genius who can perform uncommon feats, nor is he possessed of unusual powers of foresight. He is a person of normal intelligence who makes prudence a guide to his conduct. He does nothing that a prudent man would not do and does not omit to do anything a prudent man would do. He acts in accord with general and approved practice. His conduct is guided by considerations which ordinarily regulate the conduct of human affairs. His conduct is the standard "adopted in the community by persons of ordinary intelligence and prudence.
Here's a cartoon:
