@AbhishekC1725 Whenever pega does a search and get a list of results, in the run time pega uses a page of class Code-Pega-List and output will be held in pxResults. So whenever we want to search something and gets results we would need to create activity in code-pega-list class because in the run time the step page context will be code-pega-list and as activity is created in code-pega-list context pega will execute the activity which we created. For eg:- we have created a Data page and structure is List(in pega terms it is a search and get results mechanism), if you select source as activity and click on gear icon to create activity, it will be created in Code-pega-List class.

You can refer below URL also for pdn explanation

https://community.pega.com/sites/pdn.pega.com/files/help_v73/zstandardrules/rule-obj-propertycode-pega-list.htm