A term used most frequently when describing
radio controlled cars. Cars can be purchased as
kits, almost ready-to-run (ARR), which means most of the hard work is done (such as putting together the
differential and
gearbox) and ready to run (aka RTR) which means that you take it out of the box, put it on the ground and just go.
Purists of course, prefer the kit form, but in modern times, it's the ready to run that is bringing new people to radio controlled cars.