1. Third person plural or formal plural imperative/subjunctive form of 'despertarse' meaning to wake up, awaken, or rouse oneself
Wake up! (formal, plural command)
Acordem-se! (comando formal, plural)
2. Used to express urgency for multiple people to become alert or aware
Despiértense, we have an important meeting!
Acordem-se, temos uma reunião importante!