Each prefab which is compiled gets a unique id which is also referred as the "Prefab ID".
Uses of the Prefab ID
The prefab id can be used for instantiating bolt prefabs with their ID. If you would like to make a drop system for objects in your game and you want to transmit a prefab in an event then you just add a new property to your event. Let's say "ItemToDrop" and define him as "Prefab id" and then do something like: