Loose or oversteer - the rear end of the race car is coming around quicker than the front end. It feels like the rearend of the car is wagging. The car enters the turn, the driver cranks the steering wheel, and the car doesn't seem to turn quickly enough and it starts front end first going up to the top of the track. Occasionally fenders or tires will rub on opposing race cars. This is a typical thing on most short tracks.
Most drivers accept it as harmless close quarters racing.
One car tucked in behind another causes the two cars to run faster than if they were running alone. This is because the first car punches a hole in the air and the second one drives in the same whole, thus reducing aerodynamic friction for the second car. The second car also creates a advantageous effect on the first car, as it redirects the air off the back of the first car. This lightens the rearend of the first car and makes it also pick up speed. I sincerely hope this helps you understand what is being talked about during a race.