First party data (also called internal data) is data you collect on your own without any second or third party involved.
Most category leading companies are combining their internal data with external data to derive better predictions and insights.
If you share your first party data to another company (e.g. a customer or partner), it becomes second party data to them.
In the case you have an agreement with a data aggregator to monetise your data, your data becomes third party data to the customers of the data aggregator.