Some websiteRat rod is a newly developed name for the original hot rod style of the early 1950's. A rat rod is usually a vehicle that has had many of its non-critical parts removed. They are usually finished in primer-like paints and are often period correct. They are very often the conglomeration of parts and pieces of different makes and models.
A typical rat rod is an early 1930's coupe or roadster with the body set low on the frame, fenders removed, whitewall tires, big-little tire combos, exposed engine bay, home-made upholstery, and lots of power.
WikipediaRat Rod" is a style of Hot Rod or Custom car that imitates (or exaggerates) the early hot rods of the 40s, 50s, and 60s. It is not to be confused with the somewhat closely related "Traditional" Hot Rod, which is an accurate re-creation or period-correct restoration of a Hot Rod from the same era.
Most Rat Rods appear "unfinished" (whether they actually are or are not), with just the bare essentials to be driven. More recently however, a trend has arisen of making the vehicle appear "unsafe" or "scary", whether the vehicle actually is or not.
http://en.wikipedia.org/wiki/Rat_rod