How is this search keyword turned into a “key”?

I am testing my web app to pull the API from target.com; here is the API request, (I got from their site.)

https://redsky.target.com/redsky_aggregations/v1/web_platform/product_summary_with_fulfillment_v1?key=9f36aeafbe60771e321a7cc95a78140772ab3e96&tcins=15013944%2C78438139%2C53318237%2C14599316%2C54541751%2C77632333%2C81415000%2C26396441%2C16951592%2C53140802%2C17316062%2C82095690%2C51964661%2C81471842%2C14394368%2C79314666%2C14779713%2C53140800%2C54557726%2C15346395%2C79276537%2C16185593%2C79314685%2C82439935%2C53318237&store_id=666&zip=43016&state=OH&latitude=40.060&longitude=-83.150&scheduled_delivery_store_id=1969&required_store_id=666&has_required_store_id=true

What it does is to search “banana”, but it was turned into the “key”. How is this done?