Ergative case

In grammar, the ergative case (abbreviated erg) is the grammatical case that identifies a nominal phrase as the agent of a transitive verb in ergative–absolutive languages.

Comparing this with English: we use a Subject-Object model where the Subject is the "doer" and the object is the one done to. For example, a sentence like "I help him" is Subject-Noun-Object (a transitive sentence) and "He sleeps" is Subject-Noun with no object (intransitive). But in languages that use an Ergative-Absolutive model, the Ergative is used as "doer" only in a transitive sentence, otherwise the Absolutive is used. So it's like saying "I help him" (Ergative-Noun-Absolutive) but "Him sleeps" (Absolutive-Noun) (= sleeping is happening to him).