An event is one show you run in Knowhere. CES is one event. Dreamforce is one event. You build it once, invite your team, and coordinate every meeting inside it. The number of meetings does not matter.
Events count on a rolling 12 month basis. At any point, the events from your last 12 months count toward your plan. Team covers 5 and Business covers 15. If you outgrow your plan, move up a tier. Past Business, that means Enterprise, which is unlimited and custom-priced.
Team members come with the plan. Team includes 15 and Business includes 40. If your team outgrows that, add the Extra Team Member Seats add-on, a block of 10 for $19 a month. Enterprise seats are unlimited.
Managers are counted on their own. A manager builds events, sets rooms, and overrides conflicts. Team members run their own schedules. You get 2 managers on Team and 4 on Business.