開く (あく) is an intransitive verb meaning 'to open.' It describes something opening on its own, without a direct agent. For instance, 'ドアが開きます' (Doa ga akimasu) means 'The door opens.' It focuses on the state of something becoming open.

開く (あく) は「開く」という自動詞です。何かが自然に開くときに使います。「ドアが開きます」