Some activities stay dangerous no matter how careful you are, and some relationships lead the law to skip the question of fault. In these cases the injured person does not have to prove negligence. The reason behind the doctrines: when care cannot remove the risk, the party who chooses to create it, or who is made responsible for it, bears the loss.
Absolute liability, as the CDI outline uses the term, is illustrated by workers' compensation. California Labor Code §3600(a) imposes compensation liability on the employer, without regard to negligence, for injuries arising out of and in the course of employment when the statute's conditions are met. The worker does not prove fault, and an employer that followed every safety rule still owes benefits.
Strict liability examples:
Dog bites: Civil Code §3342(a) makes a dog's owner liable to a person bitten in a public place or lawfully in a private place, including the owner's property, regardless of the dog's former viciousness or the owner's knowledge of it.
Ultrahazardous activities, such as blasting: the person who engages in the activity is responsible for the harm it causes, however carefully it is carried out (CACI No. 460).
Strict liability removes the need to prove negligence, but it does not remove every defense; assumption of the risk can still apply (see the last page of this chapter). The Casualty outline gives the two textbook examples directly: an employee injured at work (absolute) and a dog bite (strict).