Antipassive

The antipassive voice (abbreviated ANTIP or AP) is a type of grammatical voice that either does not include the object or includes the object in an oblique case. This construction is similar to the passive voice, in that it decreases the verb's valency by one; the passive by deleting the subject and "promoting" the accusative object to a nominative subject, the antipassive by deleting the object and "promoting" the ergative agent to an absolutive subject. The antipassive voice is found in some Mayan, Salishan, Northeast Caucasian, Austronesian, and Australian languages. One Amazonian language, Cavineña, also has an antipassive.

The antipassive voice is found in ergative languages where the deletion of an object "demotes" the subject from ergative case to absolutive case. In certain accusative languages that have verbal agreement with both subject and object, the antipassive is usually formed by deletion of the object affix. Examples of accusative languages with this type of antipassive are Maasai, Comanche and Cahuilla. A number of direct–inverse languages also have the antipassive voice.

...
Wikipedia