The average distance between two McDonald's "restaurants" in a given city.
Since there are now more McDonald's establishments in major cities than flies in a public shitter, one can use this as a unit to measure distance in an urban environment.
Very effective for those who cannot traverse more than the said McMile without stopping to eat at McDonald's.
Person 1: What's the dis between yer home and the college?
Person 2: About 3 McMile's
Person 1: Uhh... What's a McMile?
Person 2: It's the distance between two McDonald's restaurants!
Person 1: ...
Person 1: You'd know, fatass...