Each Event sent to Mixpanel counts as a Data Point.
For example, if you are tracking the event "Purchase Item" and a customer makes a purchase, that is one data point. If customers using your application purchase 215 items, you've just sent 215 Data Points.
How do Properties impact data points?
Properties do not count toward data point totals. You can send up to 255 properties with any event at no additional cost. People properties are also not counted toward your data point total either.
When do data point allotments refresh?
Exactly when your data point allotment refreshes depends on whether you’re on a monthly or annual plan. However, at any time you can see how close you are to your plan’s limits via the Account menu.