You asked for the defination of a term that has a lot of different meanings to a lot of diffrent people.

In general the term refers to a car that has had several modifications made to enhance it's preformance usually in areas of acceleration and/or top speed.

As form follows function, there are usually visual clues when the car has been modified. Wide tires and wheels (usually with the back of the car sitting slightly higher than the front), dual exhaust, hood scoop or a blower sticking through the hood, traction bars etc etc. In a lot of cases a unique paint job (graphics. flames, racing stripes or whatever the mind can imagine) is applied, something that shouts "look at me"

BUT changes don't necessarly have to be visual from the outside of the car. A modified hi-preformance drive train under stock sheet metal with conservative tires and stock wheels and a plain paint job is still a hotrodded car (a sleeper).

I believe that M&M was referring to the visual mods.

Like most people, I can't necessarily define what a hot rod is in a 100 words or less, but I know one when I see it.