Minecraft wiki entry for JSON_format, associated text:  conditions:
 entity: The entity that was pulled. May also be a list of predicates that must pass in order for the trigger to activate.
All possible conditions for entities[show]
 item: The item that was caught.
Tags common to all items[show]
 rod: The fishing rod used.
Tags common to all items[show]
 player: The player that would get the advancement. May also be a list of predicates that must pass in order for the trigger to activate.
All possible conditions for entities[show]