A
case for marking the
subject of
transitive verbs only. The
intransitive subject and the
direct object are marked with another case, called
absolutive or
nominative. This is in contrast to the system familiar to
European speakers where the transitive and intransitive subjects share the nominative case, and the direct object is distinguished with the
accusative. Although only
Basque is ergative in Europe, the system is common and applies to about 30% of the world's
languages.
Before it was appreciated how common it was, the few ergative languages known were mis-analysed as "passive", because an active ergative sentence looks rather like the passive voice. But the ergative subject is the subject and comes first. It's not a passive agent shunted off into an oblique case.