A parameter is a key-value pair (e.g.,'currency': 'USD') that provides additional information about events or configuration settings on your page. The Google tag sends event parameters with automatically collected and recommended events already.
If you need more information about an event, you can add parameters. You can look up pre-defined parameter names or create a custom parameter, if you need it.
For example, when someone adds a product to a shopping cart, the Google tag sends an add_to_cart event. To get more detailed data on the item, you can encode parameters for that event, such as the product name, and price.