Novus actus interveniens is Latin for a new intervening act.
In a tortious claim, novus actus interveniens is the intervening act that serves to break the legal connection between the defendant’s action and the harm suffered by the plaintiff.
For example, if a defendant was negligent while driving his vehicle and had caused a collision with the plaintiff’s vehicle, he would have to pay for the damages to the plaintiff’s vehicle as well as any injuries suffered by the plaintiff. However, if the plaintiff took the vehicle that was damaged by that collision to the race track and he suffered another collision while racing and his vehicle was damaged further to the point where it was beyond repair, that novus actus interveniens would break the connection that the defendant had on the harm suffered by the plaintiff in the first collision.
Another example would be that if the same plaintiff, after the same first collision, while driving off from the accident scene, got into another collision, this time a major one which damaged his vehicle extremely badly through no fault of his own, with another vehicle, then that novus actus interveniens would also break the connection the first defendant had on the harm suffered by the plaintiff in the first collision.