Breakout rooms allow you to split your Zoom meeting into a maximum of 50 separate sessions. The meeting host can choose to split the participants of the meeting into these separate sessions automatically or manually, and can switch between sessions at any time. The host can choose to do this on the fly during the meeting or setup the breakout rooms and participants ahead of time.
Additional info and details (i.e. how many participants are allowed in each breakout room) are available in the following Zoom article: