一齐 (yī qí) means 'all together' or 'simultaneously', emphasizing that multiple subjects act in unison as a group. It differs from 同时 (tóng shí), which is a neutral 'at the same time' (often used as a conjunction), and from 一同 (yī tóng), which focuses on accompanying each other rather than acting in lockstep. 一齐 is more formal and literary than these alternatives.